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/futures-task/src/arc_wake.rs

@@ -0,0 +1,49 @@
+use alloc::sync::Arc;
+
+/// A way of waking up a specific task.
+///
+/// By implementing this trait, types that are expected to be wrapped in an `Arc`
+/// can be converted into [`Waker`] objects.
+/// Those Wakers can be used to signal executors that a task it owns
+/// is ready to be `poll`ed again.
+///
+/// Currently, there are two ways to convert `ArcWake` into [`Waker`]:
+///
+/// * [`waker`](super::waker()) converts `Arc<impl ArcWake>` into [`Waker`].
+/// * [`waker_ref`](super::waker_ref()) converts `&Arc<impl ArcWake>` into [`WakerRef`] that
+///   provides access to a [`&Waker`][`Waker`].
+///
+/// [`Waker`]: std::task::Waker
+/// [`WakerRef`]: super::WakerRef
+// Note: Send + Sync required because `Arc<T>` doesn't automatically imply
+// those bounds, but `Waker` implements them.
+pub trait ArcWake: Send + Sync {
+    /// Indicates that the associated task is ready to make progress and should
+    /// be `poll`ed.
+    ///
+    /// This function can be called from an arbitrary thread, including threads which
+    /// did not create the `ArcWake` based [`Waker`].
+    ///
+    /// Executors generally maintain a queue of "ready" tasks; `wake` should place
+    /// the associated task onto this queue.
+    ///
+    /// [`Waker`]: std::task::Waker
+    fn wake(self: Arc<Self>) {
+        Self::wake_by_ref(&self)
+    }
+
+    /// Indicates that the associated task is ready to make progress and should
+    /// be `poll`ed.
+    ///
+    /// This function can be called from an arbitrary thread, including threads which
+    /// did not create the `ArcWake` based [`Waker`].
+    ///
+    /// Executors generally maintain a queue of "ready" tasks; `wake_by_ref` should place
+    /// the associated task onto this queue.
+    ///
+    /// This function is similar to [`wake`](ArcWake::wake), but must not consume the provided data
+    /// pointer.
+    ///
+    /// [`Waker`]: std::task::Waker
+    fn wake_by_ref(arc_self: &Arc<Self>);
+}