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/anyhow/src/kind.rs

@@ -0,0 +1,121 @@
+// Tagged dispatch mechanism for resolving the behavior of `anyhow!($expr)`.
+//
+// When anyhow! is given a single expr argument to turn into anyhow::Error, we
+// want the resulting Error to pick up the input's implementation of source()
+// and backtrace() if it has a std::error::Error impl, otherwise require nothing
+// more than Display and Debug.
+//
+// Expressed in terms of specialization, we want something like:
+//
+//     trait AnyhowNew {
+//         fn new(self) -> Error;
+//     }
+//
+//     impl<T> AnyhowNew for T
+//     where
+//         T: Display + Debug + Send + Sync + 'static,
+//     {
+//         default fn new(self) -> Error {
+//             /* no std error impl */
+//         }
+//     }
+//
+//     impl<T> AnyhowNew for T
+//     where
+//         T: std::error::Error + Send + Sync + 'static,
+//     {
+//         fn new(self) -> Error {
+//             /* use std error's source() and backtrace() */
+//         }
+//     }
+//
+// Since specialization is not stable yet, instead we rely on autoref behavior
+// of method resolution to perform tagged dispatch. Here we have two traits
+// AdhocKind and TraitKind that both have an anyhow_kind() method. AdhocKind is
+// implemented whether or not the caller's type has a std error impl, while
+// TraitKind is implemented only when a std error impl does exist. The ambiguity
+// is resolved by AdhocKind requiring an extra autoref so that it has lower
+// precedence.
+//
+// The anyhow! macro will set up the call in this form:
+//
+//     #[allow(unused_imports)]
+//     use $crate::__private::{AdhocKind, TraitKind};
+//     let error = $msg;
+//     (&error).anyhow_kind().new(error)
+
+use crate::Error;
+use core::fmt::{Debug, Display};
+
+#[cfg(any(feature = "std", not(anyhow_no_core_error)))]
+use crate::StdError;
+#[cfg(any(feature = "std", not(anyhow_no_core_error)))]
+use alloc::boxed::Box;
+
+pub struct Adhoc;
+
+#[doc(hidden)]
+pub trait AdhocKind: Sized {
+    #[inline]
+    fn anyhow_kind(&self) -> Adhoc {
+        Adhoc
+    }
+}
+
+impl<T> AdhocKind for &T where T: ?Sized + Display + Debug + Send + Sync + 'static {}
+
+impl Adhoc {
+    #[cold]
+    pub fn new<M>(self, message: M) -> Error
+    where
+        M: Display + Debug + Send + Sync + 'static,
+    {
+        Error::construct_from_adhoc(message, backtrace!())
+    }
+}
+
+pub struct Trait;
+
+#[doc(hidden)]
+pub trait TraitKind: Sized {
+    #[inline]
+    fn anyhow_kind(&self) -> Trait {
+        Trait
+    }
+}
+
+impl<E> TraitKind for E where E: Into<Error> {}
+
+impl Trait {
+    #[cold]
+    pub fn new<E>(self, error: E) -> Error
+    where
+        E: Into<Error>,
+    {
+        error.into()
+    }
+}
+
+#[cfg(any(feature = "std", not(anyhow_no_core_error)))]
+pub struct Boxed;
+
+#[cfg(any(feature = "std", not(anyhow_no_core_error)))]
+#[doc(hidden)]
+pub trait BoxedKind: Sized {
+    #[inline]
+    fn anyhow_kind(&self) -> Boxed {
+        Boxed
+    }
+}
+
+#[cfg(any(feature = "std", not(anyhow_no_core_error)))]
+impl BoxedKind for Box<dyn StdError + Send + Sync> {}
+
+#[cfg(any(feature = "std", not(anyhow_no_core_error)))]
+impl Boxed {
+    #[cold]
+    pub fn new(self, error: Box<dyn StdError + Send + Sync>) -> Error {
+        let backtrace = backtrace_if_absent!(&*error);
+        Error::construct_from_boxed(error, backtrace)
+    }
+}