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/pin-project-lite/tests/ui/pinned_drop/conditional-drop-impl.rs

@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+use pin_project_lite::pin_project;
+
+// In `Drop` impl, the implementor must specify the same requirement as type definition.
+
+struct DropImpl<T> {
+    f: T,
+}
+
+impl<T: Unpin> Drop for DropImpl<T> {
+    //~^ ERROR E0367
+    fn drop(&mut self) {}
+}
+
+pin_project! {
+    //~^ ERROR E0367
+    struct PinnedDropImpl<T> {
+        #[pin]
+        f: T,
+    }
+
+    impl<T: Unpin> PinnedDrop for PinnedDropImpl<T> {
+        fn drop(_this: Pin<&mut Self>) {}
+    }
+}
+
+fn main() {}