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/proc-macro-error/tests/ui/abort.rs

@@ -0,0 +1,11 @@
+extern crate test_crate;
+use test_crate::*;
+
+abort_from!(one, two);
+abort_to_string!(one, two);
+abort_format!(one, two);
+direct_abort!(one, two);
+abort_notes!(one, two);
+abort_call_site_test!(one, two);
+
+fn main() {}