fix: resolve display stuck after disconnect and radio task deadlock

- Set disconnected flag on DisplayCommand::Reset to block stale radio
  status updates from re-rendering dashboard over splash screen
- Send StopRx to radio when USB DTR drops so radio stops generating
  packets after host disconnects
- Use try_send for unsolicited responses (RxPacket, error recovery,
  StopRx Ok) to prevent radio task deadlock on full response channel
- Fall back to LED-only event loop when display init fails instead of
  returning early and orphaning the LED

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Cargo.lock

@@ -372,7 +372,7 @@ dependencies = [
 
 [[package]]
 name = "donglora"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "cfg-if",
  "cortex-m",