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/anyhow/tests/ui/ensure-nonbool.rs

@@ -0,0 +1,40 @@
+use anyhow::{ensure, Result};
+use std::ops::{Deref, Not};
+
+struct Bool(bool);
+
+struct DerefBool(bool);
+
+struct NotBool(bool);
+
+impl Deref for DerefBool {
+    type Target = bool;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl Not for NotBool {
+    type Output = bool;
+    fn not(self) -> Self::Output {
+        !self.0
+    }
+}
+
+fn main() -> Result<()> {
+    ensure!("...");
+
+    let mut s = Bool(true);
+    match &mut s {
+        Bool(cond) => ensure!(cond),
+    }
+
+    let db = DerefBool(true);
+    ensure!(db);
+    ensure!(&db);
+
+    let nb = NotBool(true);
+    ensure!(nb);
+
+    Ok(())
+}