fix: resolve all dart analyze warnings

- Migrate RadioListTile to RadioGroup API (Flutter 3.32+)
- Guard BuildContext usage across async gaps
- Use const BorderRadius.all / EdgeInsets.all constructors
- Extract nested ternaries into helpers
- Prefer .first over [0], ??= over if-null assignment
- Prefix unused FocusNode params with _
- Add library directive for dangling doc comments

lib/services/ambient_lighting_service.dart

@@ -38,9 +38,7 @@ class AmbientLightingService {
 
     try {
       // Write static shader (only needs to happen once)
-      if (_shaderPath == null) {
-        _shaderPath = await _writeShaderToTemp(_generateShader());
-      }
+      _shaderPath ??= await _writeShaderToTemp(_generateShader());
 
       if (kDebugMode) {
         debugPrint('AmbientLightingService: Shader path: $_shaderPath');

lib/services/external_player_service.dart

@@ -47,7 +47,7 @@ class ExternalPlayerService {
       final player = settings.getSelectedExternalPlayer();
 
       // On Android, always use native intent to avoid url_launcher opening in browser
-      if (Platform.isAndroid) {
+      if (Platform.isAndroid && context.mounted) {
         return _launchAndroidNative(resolvedUrl, player, context);
       }