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-time/src/driver_mock.rs

@@ -0,0 +1,221 @@
+use core::cell::RefCell;
+
+use critical_section::Mutex as CsMutex;
+use embassy_time_driver::{AlarmHandle, Driver};
+
+use crate::{Duration, Instant};
+
+/// A mock driver that can be manually advanced.
+/// This is useful for testing code that works with [`Instant`] and [`Duration`].
+///
+/// This driver can also be used to test runtime functionality, such as
+/// timers, delays, etc.
+///
+/// # Example
+///
+/// ```ignore
+/// fn has_a_second_passed(reference: Instant) -> bool {
+///     Instant::now().duration_since(reference) >= Duration::from_secs(1)
+/// }
+///
+/// fn test_second_passed() {
+///     let driver = embassy_time::MockDriver::get();
+///     let reference = Instant::now();
+///     assert_eq!(false, has_a_second_passed(reference));
+///     driver.advance(Duration::from_secs(1));
+///     assert_eq!(true, has_a_second_passed(reference));
+/// }
+/// ```
+pub struct MockDriver(CsMutex<RefCell<InnerMockDriver>>);
+
+embassy_time_driver::time_driver_impl!(static DRIVER: MockDriver = MockDriver::new());
+
+impl MockDriver {
+    /// Creates a new mock driver.
+    pub const fn new() -> Self {
+        Self(CsMutex::new(RefCell::new(InnerMockDriver::new())))
+    }
+
+    /// Gets a reference to the global mock driver.
+    pub fn get() -> &'static MockDriver {
+        &DRIVER
+    }
+
+    /// Resets the internal state of the mock driver
+    /// This will clear and deallocate all alarms, and reset the current time to 0.
+    pub fn reset(&self) {
+        critical_section::with(|cs| {
+            self.0.borrow(cs).replace(InnerMockDriver::new());
+        });
+    }
+
+    /// Advances the time by the specified [`Duration`].
+    /// Calling any alarm callbacks that are due.
+    pub fn advance(&self, duration: Duration) {
+        let notify = {
+            critical_section::with(|cs| {
+                let mut inner = self.0.borrow_ref_mut(cs);
+
+                inner.now += duration;
+
+                let now = inner.now.as_ticks();
+
+                inner
+                    .alarm
+                    .as_mut()
+                    .filter(|alarm| alarm.timestamp <= now)
+                    .map(|alarm| {
+                        alarm.timestamp = u64::MAX;
+
+                        (alarm.callback, alarm.ctx)
+                    })
+            })
+        };
+
+        if let Some((callback, ctx)) = notify {
+            (callback)(ctx);
+        }
+    }
+}
+
+impl Driver for MockDriver {
+    fn now(&self) -> u64 {
+        critical_section::with(|cs| self.0.borrow_ref(cs).now).as_ticks()
+    }
+
+    unsafe fn allocate_alarm(&self) -> Option<AlarmHandle> {
+        critical_section::with(|cs| {
+            let mut inner = self.0.borrow_ref_mut(cs);
+
+            if inner.alarm.is_some() {
+                None
+            } else {
+                inner.alarm.replace(AlarmState::new());
+
+                Some(AlarmHandle::new(0))
+            }
+        })
+    }
+
+    fn set_alarm_callback(&self, _alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ()) {
+        critical_section::with(|cs| {
+            let mut inner = self.0.borrow_ref_mut(cs);
+
+            let Some(alarm) = inner.alarm.as_mut() else {
+                panic!("Alarm not allocated");
+            };
+
+            alarm.callback = callback;
+            alarm.ctx = ctx;
+        });
+    }
+
+    fn set_alarm(&self, _alarm: AlarmHandle, timestamp: u64) -> bool {
+        critical_section::with(|cs| {
+            let mut inner = self.0.borrow_ref_mut(cs);
+
+            if timestamp <= inner.now.as_ticks() {
+                false
+            } else {
+                let Some(alarm) = inner.alarm.as_mut() else {
+                    panic!("Alarm not allocated");
+                };
+
+                alarm.timestamp = timestamp;
+                true
+            }
+        })
+    }
+}
+
+struct InnerMockDriver {
+    now: Instant,
+    alarm: Option<AlarmState>,
+}
+
+impl InnerMockDriver {
+    const fn new() -> Self {
+        Self {
+            now: Instant::from_ticks(0),
+            alarm: None,
+        }
+    }
+}
+
+struct AlarmState {
+    timestamp: u64,
+    callback: fn(*mut ()),
+    ctx: *mut (),
+}
+
+impl AlarmState {
+    const fn new() -> Self {
+        Self {
+            timestamp: u64::MAX,
+            callback: Self::noop,
+            ctx: core::ptr::null_mut(),
+        }
+    }
+
+    fn noop(_ctx: *mut ()) {}
+}
+
+unsafe impl Send for AlarmState {}
+
+#[cfg(test)]
+mod tests {
+    use serial_test::serial;
+
+    use super::*;
+
+    fn setup() {
+        DRIVER.reset();
+    }
+
+    #[test]
+    #[serial]
+    fn test_advance() {
+        setup();
+
+        let driver = MockDriver::get();
+        let reference = driver.now();
+        driver.advance(Duration::from_secs(1));
+        assert_eq!(Duration::from_secs(1).as_ticks(), driver.now() - reference);
+    }
+
+    #[test]
+    #[serial]
+    fn test_set_alarm_not_in_future() {
+        setup();
+
+        let driver = MockDriver::get();
+        let alarm = unsafe { AlarmHandle::new(0) };
+        assert_eq!(false, driver.set_alarm(alarm, driver.now()));
+    }
+
+    #[test]
+    #[serial]
+    fn test_alarm() {
+        setup();
+
+        let driver = MockDriver::get();
+        let alarm = unsafe { driver.allocate_alarm() }.expect("No alarms available");
+        static mut CALLBACK_CALLED: bool = false;
+        let ctx = &mut () as *mut ();
+        driver.set_alarm_callback(alarm, |_| unsafe { CALLBACK_CALLED = true }, ctx);
+        driver.set_alarm(alarm, driver.now() + 1);
+        assert_eq!(false, unsafe { CALLBACK_CALLED });
+        driver.advance(Duration::from_secs(1));
+        assert_eq!(true, unsafe { CALLBACK_CALLED });
+    }
+
+    #[test]
+    #[serial]
+    fn test_allocate_alarm() {
+        setup();
+
+        let driver = MockDriver::get();
+        assert!(unsafe { driver.allocate_alarm() }.is_some());
+        assert!(unsafe { driver.allocate_alarm() }.is_none());
+    }
+}