feat: add display UI with splash screen, dashboard, and RSSI sparkline

Implement full SSD1306 OLED display support:
- Splash screen on boot (1.5s) with project name, version, board
- Dashboard showing radio state, config, counters, RSSI/SNR
- RSSI history sparkline (64-sample ring buffer, 2px-wide bars)
- DisplayOn/DisplayOff host commands routed via dedicated channel
- Pure render functions against generic DrawTarget (no hardware coupling)
- Display on/off control bypasses radio task entirely

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/embassy-sync/src/mutex.rs

@@ -0,0 +1,392 @@
+//! Async mutex.
+//!
+//! This module provides a mutex that can be used to synchronize data between asynchronous tasks.
+use core::cell::{RefCell, UnsafeCell};
+use core::future::{poll_fn, Future};
+use core::ops::{Deref, DerefMut};
+use core::task::Poll;
+use core::{fmt, mem};
+
+use crate::blocking_mutex::raw::RawMutex;
+use crate::blocking_mutex::Mutex as BlockingMutex;
+use crate::waitqueue::WakerRegistration;
+
+/// Error returned by [`Mutex::try_lock`]
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub struct TryLockError;
+
+#[derive(Debug)]
+struct State {
+    locked: bool,
+    waker: WakerRegistration,
+}
+
+/// Async mutex.
+///
+/// The mutex is generic over a blocking [`RawMutex`].
+/// The raw mutex is used to guard access to the internal "is locked" flag. It
+/// is held for very short periods only, while locking and unlocking. It is *not* held
+/// for the entire time the async Mutex is locked.
+///
+/// Which implementation you select depends on the context in which you're using the mutex.
+///
+/// Use [`CriticalSectionRawMutex`](crate::blocking_mutex::raw::CriticalSectionRawMutex) when data can be shared between threads and interrupts.
+///
+/// Use [`NoopRawMutex`](crate::blocking_mutex::raw::NoopRawMutex) when data is only shared between tasks running on the same executor.
+///
+/// Use [`ThreadModeRawMutex`](crate::blocking_mutex::raw::ThreadModeRawMutex) when data is shared between tasks running on the same executor but you want a singleton.
+///
+pub struct Mutex<M, T>
+where
+    M: RawMutex,
+    T: ?Sized,
+{
+    state: BlockingMutex<M, RefCell<State>>,
+    inner: UnsafeCell<T>,
+}
+
+unsafe impl<M: RawMutex + Send, T: ?Sized + Send> Send for Mutex<M, T> {}
+unsafe impl<M: RawMutex + Sync, T: ?Sized + Send> Sync for Mutex<M, T> {}
+
+/// Async mutex.
+impl<M, T> Mutex<M, T>
+where
+    M: RawMutex,
+{
+    /// Create a new mutex with the given value.
+    pub const fn new(value: T) -> Self {
+        Self {
+            inner: UnsafeCell::new(value),
+            state: BlockingMutex::new(RefCell::new(State {
+                locked: false,
+                waker: WakerRegistration::new(),
+            })),
+        }
+    }
+}
+
+impl<M, T> Mutex<M, T>
+where
+    M: RawMutex,
+    T: ?Sized,
+{
+    /// Lock the mutex.
+    ///
+    /// This will wait for the mutex to be unlocked if it's already locked.
+    pub fn lock(&self) -> impl Future<Output = MutexGuard<'_, M, T>> {
+        poll_fn(|cx| {
+            let ready = self.state.lock(|s| {
+                let mut s = s.borrow_mut();
+                if s.locked {
+                    s.waker.register(cx.waker());
+                    false
+                } else {
+                    s.locked = true;
+                    true
+                }
+            });
+
+            if ready {
+                Poll::Ready(MutexGuard { mutex: self })
+            } else {
+                Poll::Pending
+            }
+        })
+    }
+
+    /// Attempt to immediately lock the mutex.
+    ///
+    /// If the mutex is already locked, this will return an error instead of waiting.
+    pub fn try_lock(&self) -> Result<MutexGuard<'_, M, T>, TryLockError> {
+        self.state.lock(|s| {
+            let mut s = s.borrow_mut();
+            if s.locked {
+                Err(TryLockError)
+            } else {
+                s.locked = true;
+                Ok(())
+            }
+        })?;
+
+        Ok(MutexGuard { mutex: self })
+    }
+
+    /// Consumes this mutex, returning the underlying data.
+    pub fn into_inner(self) -> T
+    where
+        T: Sized,
+    {
+        self.inner.into_inner()
+    }
+
+    /// Returns a mutable reference to the underlying data.
+    ///
+    /// Since this call borrows the Mutex mutably, no actual locking needs to
+    /// take place -- the mutable borrow statically guarantees no locks exist.
+    pub fn get_mut(&mut self) -> &mut T {
+        self.inner.get_mut()
+    }
+}
+
+impl<M: RawMutex, T> From<T> for Mutex<M, T> {
+    fn from(from: T) -> Self {
+        Self::new(from)
+    }
+}
+
+impl<M, T> Default for Mutex<M, T>
+where
+    M: RawMutex,
+    T: Default,
+{
+    fn default() -> Self {
+        Self::new(Default::default())
+    }
+}
+
+impl<M, T> fmt::Debug for Mutex<M, T>
+where
+    M: RawMutex,
+    T: ?Sized + fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut d = f.debug_struct("Mutex");
+        match self.try_lock() {
+            Ok(value) => {
+                d.field("inner", &&*value);
+            }
+            Err(TryLockError) => {
+                d.field("inner", &format_args!("<locked>"));
+            }
+        }
+
+        d.finish_non_exhaustive()
+    }
+}
+
+/// Async mutex guard.
+///
+/// Owning an instance of this type indicates having
+/// successfully locked the mutex, and grants access to the contents.
+///
+/// Dropping it unlocks the mutex.
+#[clippy::has_significant_drop]
+#[must_use = "if unused the Mutex will immediately unlock"]
+pub struct MutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized,
+{
+    mutex: &'a Mutex<M, T>,
+}
+
+impl<'a, M, T> MutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized,
+{
+    /// Returns a locked view over a portion of the locked data.
+    pub fn map<U>(this: Self, fun: impl FnOnce(&mut T) -> &mut U) -> MappedMutexGuard<'a, M, U> {
+        let mutex = this.mutex;
+        let value = fun(unsafe { &mut *this.mutex.inner.get() });
+        // Don't run the `drop` method for MutexGuard. The ownership of the underlying
+        // locked state is being moved to the returned MappedMutexGuard.
+        mem::forget(this);
+        MappedMutexGuard {
+            state: &mutex.state,
+            value,
+        }
+    }
+}
+
+impl<'a, M, T> Drop for MutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized,
+{
+    fn drop(&mut self) {
+        self.mutex.state.lock(|s| {
+            let mut s = unwrap!(s.try_borrow_mut());
+            s.locked = false;
+            s.waker.wake();
+        })
+    }
+}
+
+impl<'a, M, T> Deref for MutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized,
+{
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        // Safety: the MutexGuard represents exclusive access to the contents
+        // of the mutex, so it's OK to get it.
+        unsafe { &*(self.mutex.inner.get() as *const T) }
+    }
+}
+
+impl<'a, M, T> DerefMut for MutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized,
+{
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        // Safety: the MutexGuard represents exclusive access to the contents
+        // of the mutex, so it's OK to get it.
+        unsafe { &mut *(self.mutex.inner.get()) }
+    }
+}
+
+impl<'a, M, T> fmt::Debug for MutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized + fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, M, T> fmt::Display for MutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized + fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+/// A handle to a held `Mutex` that has had a function applied to it via [`MutexGuard::map`] or
+/// [`MappedMutexGuard::map`].
+///
+/// This can be used to hold a subfield of the protected data.
+#[clippy::has_significant_drop]
+pub struct MappedMutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized,
+{
+    state: &'a BlockingMutex<M, RefCell<State>>,
+    value: *mut T,
+}
+
+impl<'a, M, T> MappedMutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized,
+{
+    /// Returns a locked view over a portion of the locked data.
+    pub fn map<U>(this: Self, fun: impl FnOnce(&mut T) -> &mut U) -> MappedMutexGuard<'a, M, U> {
+        let state = this.state;
+        let value = fun(unsafe { &mut *this.value });
+        // Don't run the `drop` method for MutexGuard. The ownership of the underlying
+        // locked state is being moved to the returned MappedMutexGuard.
+        mem::forget(this);
+        MappedMutexGuard { state, value }
+    }
+}
+
+impl<'a, M, T> Deref for MappedMutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized,
+{
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        // Safety: the MutexGuard represents exclusive access to the contents
+        // of the mutex, so it's OK to get it.
+        unsafe { &*self.value }
+    }
+}
+
+impl<'a, M, T> DerefMut for MappedMutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized,
+{
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        // Safety: the MutexGuard represents exclusive access to the contents
+        // of the mutex, so it's OK to get it.
+        unsafe { &mut *self.value }
+    }
+}
+
+impl<'a, M, T> Drop for MappedMutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized,
+{
+    fn drop(&mut self) {
+        self.state.lock(|s| {
+            let mut s = unwrap!(s.try_borrow_mut());
+            s.locked = false;
+            s.waker.wake();
+        })
+    }
+}
+
+unsafe impl<M, T> Send for MappedMutexGuard<'_, M, T>
+where
+    M: RawMutex + Sync,
+    T: Send + ?Sized,
+{
+}
+
+unsafe impl<M, T> Sync for MappedMutexGuard<'_, M, T>
+where
+    M: RawMutex + Sync,
+    T: Sync + ?Sized,
+{
+}
+
+impl<'a, M, T> fmt::Debug for MappedMutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized + fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, M, T> fmt::Display for MappedMutexGuard<'a, M, T>
+where
+    M: RawMutex,
+    T: ?Sized + fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::blocking_mutex::raw::NoopRawMutex;
+    use crate::mutex::{Mutex, MutexGuard};
+
+    #[futures_test::test]
+    async fn mapped_guard_releases_lock_when_dropped() {
+        let mutex: Mutex<NoopRawMutex, [i32; 2]> = Mutex::new([0, 1]);
+
+        {
+            let guard = mutex.lock().await;
+            assert_eq!(*guard, [0, 1]);
+            let mut mapped = MutexGuard::map(guard, |this| &mut this[1]);
+            assert_eq!(*mapped, 1);
+            *mapped = 2;
+        }
+
+        {
+            let guard = mutex.lock().await;
+            assert_eq!(*guard, [0, 2]);
+            let mut mapped = MutexGuard::map(guard, |this| &mut this[1]);
+            assert_eq!(*mapped, 2);
+            *mapped = 3;
+        }
+
+        assert_eq!(*mutex.lock().await, [0, 3]);
+    }
+}