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-queue-driver/src/lib.rs

@@ -0,0 +1,60 @@
+#![no_std]
+#![doc = include_str!("../README.md")]
+#![warn(missing_docs)]
+
+//! ## Implementing a timer queue
+//!
+//! - Define a struct `MyTimerQueue`
+//! - Implement [`TimerQueue`] for it
+//! - Register it as the global timer queue with [`timer_queue_impl`](crate::timer_queue_impl).
+//!
+//! ## Example
+//!
+//! ```
+//! use core::task::Waker;
+//!
+//! use embassy_time::Instant;
+//! use embassy_time::queue::{TimerQueue};
+//!
+//! struct MyTimerQueue{}; // not public!
+//!
+//! impl TimerQueue for MyTimerQueue {
+//!     fn schedule_wake(&'static self, at: u64, waker: &Waker) {
+//!         todo!()
+//!     }
+//! }
+//!
+//! embassy_time_queue_driver::timer_queue_impl!(static QUEUE: MyTimerQueue = MyTimerQueue{});
+//! ```
+use core::task::Waker;
+
+/// Timer queue
+pub trait TimerQueue {
+    /// Schedules a waker in the queue to be awoken at moment `at`.
+    /// If this moment is in the past, the waker might be awoken immediately.
+    fn schedule_wake(&'static self, at: u64, waker: &Waker);
+}
+
+extern "Rust" {
+    fn _embassy_time_schedule_wake(at: u64, waker: &Waker);
+}
+
+/// Schedule the given waker to be woken at `at`.
+pub fn schedule_wake(at: u64, waker: &Waker) {
+    unsafe { _embassy_time_schedule_wake(at, waker) }
+}
+
+/// Set the TimerQueue implementation.
+///
+/// See the module documentation for an example.
+#[macro_export]
+macro_rules! timer_queue_impl {
+    (static $name:ident: $t: ty = $val:expr) => {
+        static $name: $t = $val;
+
+        #[no_mangle]
+        fn _embassy_time_schedule_wake(at: u64, waker: &core::task::Waker) {
+            <$t as $crate::TimerQueue>::schedule_wake(&$name, at, waker);
+        }
+    };
+}