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/models/companion_radio_stats.dart

@@ -0,0 +1,48 @@
+import 'dart:typed_data';
+
+import '../connector/meshcore_protocol.dart';
+import '../utils/app_logger.dart';
+
+/// Parsed `RESP_CODE_STATS` + `STATS_TYPE_RADIO` (14 bytes total).
+class CompanionRadioStats {
+  final int noiseFloorDbm;
+  final int lastRssiDbm;
+  final double lastSnrDb;
+  final int txAirSecs;
+  final int rxAirSecs;
+  final DateTime receivedAt;
+
+  const CompanionRadioStats({
+    required this.noiseFloorDbm,
+    required this.lastRssiDbm,
+    required this.lastSnrDb,
+    required this.txAirSecs,
+    required this.rxAirSecs,
+    required this.receivedAt,
+  });
+
+  static CompanionRadioStats? tryParse(Uint8List frame) {
+    if (frame.length < 14) return null;
+    if (frame[0] != respCodeStats || frame[1] != statsTypeRadio) return null;
+    try {
+      final reader = BufferReader(frame);
+      reader.skipBytes(2);
+      final noise = reader.readInt16LE();
+      final rssi = reader.readInt8();
+      final snrRaw = reader.readInt8();
+      final txAir = reader.readUInt32LE();
+      final rxAir = reader.readUInt32LE();
+      return CompanionRadioStats(
+        noiseFloorDbm: noise,
+        lastRssiDbm: rssi,
+        lastSnrDb: snrRaw / 4.0,
+        txAirSecs: txAir,
+        rxAirSecs: rxAir,
+        receivedAt: DateTime.now(),
+      );
+    } catch (e) {
+      appLogger.warn('CompanionRadioStats parse error: $e');
+      return null;
+    }
+  }
+}