Add LPCNet voice mode support

lib/screens/settings_screen.dart

@@ -18,8 +18,8 @@ import '../services/location_tracking_service.dart';
 import '../services/locale_preferences.dart';
 import '../services/mesh_map_nodes_service.dart';
 import '../services/update_checker_service.dart';
-import '../services/voice_codec_service.dart';
 import '../services/voice_bitrate_preferences.dart';
+import '../services/voice_codec_preferences.dart';
 import '../services/image_preferences.dart';
 import '../services/route_hash_preferences.dart';
 import '../services/image_codec_service.dart';
@@ -60,6 +60,7 @@ class _SettingsScreenState extends State<SettingsScreen> {
   bool _showRxTxIndicators = true;
   bool _isCheckingForUpdates = false;
   int _voiceBitrate = VoiceBitratePreferences.defaultBitrate;
+  VoiceCodecKind _voiceCodec = VoiceCodecPreferences.defaultCodec;
   int _routeHashSize = RouteHashPreferences.defaultHashSize;
   int _imageMaxSize = ImagePreferences.defaultMaxSize;
   int _imageCompression = ImagePreferences.defaultQuality;
@@ -88,7 +89,7 @@ class _SettingsScreenState extends State<SettingsScreen> {
     _loadPackageInfo();
     _initializeLocationService();
     _loadRxTxPreference();
-    _loadVoiceBitratePreference();
+    _loadVoicePreferences();
     _loadRouteHashSizePreference();
     _loadImagePreferences();
     _loadFastLocationSettings();
@@ -178,11 +179,13 @@ class _SettingsScreenState extends State<SettingsScreen> {
     await prefs.setBool('show_rx_tx_indicators', value);
   }
 
-  Future<void> _loadVoiceBitratePreference() async {
+  Future<void> _loadVoicePreferences() async {
     final value = await VoiceBitratePreferences.getBitrate();
+    final codec = await VoiceCodecPreferences.getCodec();
     if (!mounted) return;
     setState(() {
       _voiceBitrate = value;
+      _voiceCodec = codec;
     });
   }
 
@@ -194,10 +197,27 @@ class _SettingsScreenState extends State<SettingsScreen> {
     });
   }
 
+  Future<void> _saveVoiceCodecPreference(VoiceCodecKind value) async {
+    await VoiceCodecPreferences.setCodec(value);
+    if (!mounted) return;
+    setState(() {
+      _voiceCodec = value;
+    });
+  }
+
   String _voiceBitrateSubtitle(int bitrate) {
+    if (_voiceCodec == VoiceCodecKind.lpcnet) {
+      return 'Fixed 1600 bps';
+    }
     return '$bitrate bps';
   }
 
+  String _voiceCodecSubtitle() {
+    return _voiceCodec == VoiceCodecKind.codec2
+        ? 'Selectable low-bitrate modes'
+        : 'Fixed 16 kHz / 1.6 kbps mode';
+  }
+
   Future<void> _loadRouteHashSizePreference() async {
     final value = await RouteHashPreferences.getHashSize();
     if (!mounted) return;
@@ -1159,6 +1179,7 @@ class _SettingsScreenState extends State<SettingsScreen> {
           Consumer2<AppProvider, ConnectionProvider>(
             builder: (context, appProvider, connectionProvider, child) =>
                 _buildVoiceStatsCard(
+                  codec: _voiceCodec,
                   bitrate: _voiceBitrate,
                   connectionProvider: connectionProvider,
                   bandPassEnabled: appProvider.isVoiceBandPassFilterEnabled,
@@ -1168,12 +1189,22 @@ class _SettingsScreenState extends State<SettingsScreen> {
                 ),
           ),
           _buildSettingsCard([
+            ListTile(
+              leading: const Icon(Icons.record_voice_over),
+              title: const Text('Voice codec'),
+              subtitle: Text(_voiceCodecSubtitle()),
+              trailing: const Icon(Icons.chevron_right),
+              onTap: _showVoiceCodecDialog,
+            ),
             ListTile(
               leading: const Icon(Icons.graphic_eq),
               title: const Text('Voice bitrate'),
               subtitle: Text(_voiceBitrateSubtitle(_voiceBitrate)),
               trailing: const Icon(Icons.chevron_right),
-              onTap: _showVoiceBitrateDialog,
+              enabled: _voiceCodec == VoiceCodecKind.codec2,
+              onTap: _voiceCodec == VoiceCodecKind.codec2
+                  ? _showVoiceBitrateDialog
+                  : null,
             ),
             Consumer<AppProvider>(
               builder: (context, appProvider, child) => SwitchListTile(
@@ -1724,6 +1755,7 @@ class _SettingsScreenState extends State<SettingsScreen> {
   }
 
   Widget _buildVoiceStatsCard({
+    required VoiceCodecKind codec,
     required int bitrate,
     required ConnectionProvider connectionProvider,
     required bool bandPassEnabled,
@@ -1746,9 +1778,11 @@ class _SettingsScreenState extends State<SettingsScreen> {
     final radioSf = connectionProvider.deviceInfo.radioSf;
     final radioCr = connectionProvider.deviceInfo.radioCr;
     final bwHz = _resolveBandwidthHz(radioBw);
-    final voiceMode = VoiceBitratePreferences.toVoiceMode(bitrate);
+    final voiceMode = codec == VoiceCodecKind.lpcnet
+        ? VoicePacketMode.lpcnet1600
+        : VoiceBitratePreferences.toVoiceMode(bitrate);
     const voicePreviewMs = 10000; // 10-second reference clip
-    final packetDurationMs = codec2ModeFor(voiceMode).packetDurationMs;
+    final packetDurationMs = voiceMode.packetDurationMs;
     final voicePacketCount =
         (voicePreviewMs + packetDurationMs - 1) ~/ packetDurationMs;
     final voiceDirect = estimateVoiceTransmitDuration(
@@ -1783,7 +1817,7 @@ class _SettingsScreenState extends State<SettingsScreen> {
             ),
             const SizedBox(height: 8),
             Text(
-              'Bitrate: $bitrate bps',
+              'Codec: ${voiceMode.label}${codec == VoiceCodecKind.codec2 ? ' · $bitrate bps' : ' · 1600 bps'}',
               style: Theme.of(context).textTheme.bodySmall,
             ),
             const SizedBox(height: 4),
@@ -2112,6 +2146,47 @@ class _SettingsScreenState extends State<SettingsScreen> {
     );
   }
 
+  void _showVoiceCodecDialog() {
+    showDialog(
+      context: context,
+      builder: (context) => AlertDialog(
+        title: const Text('Voice codec'),
+        content: SingleChildScrollView(
+          child: RadioGroup<VoiceCodecKind>(
+            groupValue: _voiceCodec,
+            onChanged: (value) {
+              if (value != null) {
+                _saveVoiceCodecPreference(value);
+              }
+              Navigator.pop(context);
+            },
+            child: Column(
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                RadioListTile<VoiceCodecKind>(
+                  value: VoiceCodecKind.codec2,
+                  title: const Text('Codec2'),
+                  subtitle: const Text('Selectable ultra-low bitrate modes'),
+                ),
+                RadioListTile<VoiceCodecKind>(
+                  value: VoiceCodecKind.lpcnet,
+                  title: const Text('LPCNet'),
+                  subtitle: const Text('Fixed 16 kHz / 1.6 kbps neural mode'),
+                ),
+              ],
+            ),
+          ),
+        ),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.pop(context),
+            child: Text(AppLocalizations.of(context)!.cancel),
+          ),
+        ],
+      ),
+    );
+  }
+
   void _showAboutDialog() {
     showDialog(
       context: context,