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/object/tests/parse_self.rs

@@ -0,0 +1,25 @@
+#![cfg(feature = "read")]
+use object::{File, Object};
+use std::{env, fs};
+
+#[test]
+fn parse_self() {
+    let exe = env::current_exe().unwrap();
+    let data = fs::read(exe).unwrap();
+    let object = File::parse(&*data).unwrap();
+    assert!(object.entry() != 0);
+    assert!(object.sections().count() != 0);
+}
+
+#[cfg(feature = "std")]
+#[test]
+fn parse_self_cache() {
+    use object::read::{ReadCache, ReadRef};
+    let exe = env::current_exe().unwrap();
+    let file = fs::File::open(exe).unwrap();
+    let cache = ReadCache::new(file);
+    let data = cache.range(0, cache.len().unwrap());
+    let object = File::parse(data).unwrap();
+    assert!(object.entry() != 0);
+    assert!(object.sections().count() != 0);
+}