Add companion radio stats, adaptive backoff, path hash width, and UI improvements

- Companion radio stats: poll and display noise floor, RSSI, SNR, airtime
  with dedicated ValueNotifier and ref-counted polling
- Adaptive RF-aware TX backoff based on radio conditions instead of fixed 5s
- Variable-width path hash support (1-3 bytes per hop)
- Air activity dot indicator in app bar with tap to open stats screen
- Jump to oldest unread setting for chat screens
- 1s send cooldown on DM and channel messages
- Link style: theme-aware orange, added EmailLinkifier
- New languages: Hungarian, Japanese, Korean
- Remove dead DeviceScreen and BatteryIndicatorChip
- Remove wakelock_plus dependency
- TX power fields now read as signed int8

lib/screens/chat_screen.dart

@@ -613,9 +613,9 @@ class _ChatScreenState extends State<ChatScreen> {
     final now = DateTime.now();
     if (_lastTextSendAt != null &&
         now.difference(_lastTextSendAt!) < const Duration(seconds: 1)) {
-      ScaffoldMessenger.of(context).showSnackBar(
-        SnackBar(content: Text(context.l10n.chat_sendCooldown)),
-      );
+      ScaffoldMessenger.of(
+        context,
+      ).showSnackBar(SnackBar(content: Text(context.l10n.chat_sendCooldown)));
       return;
     }
     _lastTextSendAt = now;