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/unicode-ident/tests/fst/.gitignore

@@ -0,0 +1 @@
+/prop_list.rs

vendor/unicode-ident/tests/fst/mod.rs

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+#![allow(clippy::module_name_repetitions)]
+
+pub fn xid_start_fst() -> fst::Set<&'static [u8]> {
+    let data = include_bytes!("xid_start.fst");
+    fst::Set::from(fst::raw::Fst::new(data.as_slice()).unwrap())
+}
+
+pub fn xid_continue_fst() -> fst::Set<&'static [u8]> {
+    let data = include_bytes!("xid_continue.fst");
+    fst::Set::from(fst::raw::Fst::new(data.as_slice()).unwrap())
+}