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/auxiliary/mod.rs

@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+#![allow(dead_code, unused_macros)]
+
+macro_rules! assert_unpin {
+    ($ty:ty) => {
+        static_assertions::assert_impl_all!($ty: Unpin);
+    };
+}
+macro_rules! assert_not_unpin {
+    ($ty:ty) => {
+        static_assertions::assert_not_impl_all!($ty: Unpin);
+    };
+}