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/zerocopy/benches/try_read_from_bytes.rs

@@ -0,0 +1,7 @@
+#[path = "formats/coco_static_size.rs"]
+mod format;
+
+#[unsafe(no_mangle)]
+fn bench_try_read_from_bytes_static_size(source: &[u8]) -> Option<format::CocoPacket> {
+    zerocopy::TryFromBytes::try_read_from_bytes(source).ok()
+}