feat: Modernisation UI/UX et configuration Flutter multi-plateforme

Phase 1 - Corrections Critiques:
- Fixed memory leaks dans music_provider.dart (stream subscriptions)
- Fixed race conditions dans search_provider.dart (stale results)
- Fixed token refresh errors dans api_service.dart
- Improved error handling avec messages utilisateur
- Changed API URL to HTTPS by default

Phase 2 - Améliorations UX Desktop:
- Ajouté cursor pointers sur tous les éléments cliquables
- Implémenté hover states avec effets néon glow (200ms transitions)
- Créé skeleton loading states avec shimmer animation
- Ajouté widgets: ClickableWrapper, ErrorDisplay, SkeletonLoading
- Enhanced visual feedback pour desktop users

Phase 3 - Configuration Flutter:
- Configuré Android (Gradle 8.1.0, Kotlin 1.9.0, minSdk 21, targetSdk 34)
- Créé launcher icons cyberpunk néon (5 densités)
- Configuré Windows desktop (structure complète)
- Activé Linux desktop support
- Ajouté package équatable pour entités de domaine
- Corrigé imports (colors.dart, auth_provider.dart)
- Fixed Dio API compatibility (RequestOptions)

Documentation:
- STYLE_GUIDE.md: Guide complet (100+ pages)
- DESIGN_IMPLEMENTATION_GUIDE.md: Implémentation Flutter
- BUILD_STATUS.md: Status builds + troubleshooting
- QUICKSTART_BUILDS.md: Guide rapide
- BUILD_INDEX.md: Index documentation
- PHASE_1_CORRECTIONS.md: Corrections Phase 1
- PHASE_2_UX_IMPROVEMENTS.md: Améliorations Phase 2
- PR_REVIEW_SUMMARY.md: Revue code complète
- CODE_ANALYSIS_AND_PRIORITIES.md: Analyse code

Scripts & Builds:
- BUILD_ALL.sh: Script automatisé builds multi-plateforme
- builds/: Structure avec README par plateforme
- design-system/: Système de design complet

Backend:
- Ajouté streaming HTTP Range pour audio progressif
- Enhanced YouTube service avec métadonnées complètes
- Improved error handling et validation

Generated with [Claude Code](https://claude.com/claude-code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

frontend/lib/presentation/providers/music_provider.dart

@@ -1,6 +1,9 @@
 /// Music Provider - Player state management
 library;
 
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:just_audio/just_audio.dart';
 
@@ -56,44 +59,65 @@ class PlayerState {
 class PlayerNotifier extends StateNotifier<PlayerState> {
   PlayerNotifier() : super(const PlayerState()) {
     _player = AudioPlayer();
+    _subscriptions = [];
     _init();
   }
 
   late final AudioPlayer _player;
+  final List<StreamSubscription> _subscriptions = [];
 
   void _init() {
-    _player.positionStream.listen((position) {
+    // Subscribe to position stream and store subscription
+    _subscriptions.add(_player.positionStream.listen((position) {
       state = state.copyWith(position: position);
-    });
+    }));
 
-    _player.durationStream.listen((duration) {
+    // Subscribe to duration stream and store subscription
+    _subscriptions.add(_player.durationStream.listen((duration) {
       state = state.copyWith(duration: duration ?? Duration.zero);
-    });
+    }));
 
-    _player.playerStateStream.listen((playerState) {
+    // Subscribe to player state stream and store subscription
+    _subscriptions.add(_player.playerStateStream.listen((playerState) {
       state = state.copyWith(
         isPlaying: playerState.playing,
         isLoading: playerState.processingState == ProcessingState.loading,
       );
-    });
+    }));
   }
 
   Future<void> loadTrack(Track track) async {
-    state = state.copyWith(isLoading: true);
+    state = state.copyWith(isLoading: true, errorMessage: null);
 
     try {
-      // Get stream URL from API
-      final streamUrl = track.audioUrl ?? '';
+      // Validate audio URL exists
+      final streamUrl = track.audioUrl;
+
+      if (streamUrl == null || streamUrl.isEmpty) {
+        throw Exception('No audio URL available for track: ${track.title}');
+      }
 
       await _player.setUrl(streamUrl);
 
       if (state.queue.isEmpty) {
         state = state.copyWith(queue: [track], currentIndex: 0);
       }
-    } catch (e) {
+
+      // Clear error and loading state on success
+      state = state.copyWith(isLoading: false, errorMessage: null);
+    } on PlayerException catch (e) {
+      // Specific audio player errors
+      debugPrint('Player error loading track: ${e.message}');
       state = state.copyWith(
         isLoading: false,
-        errorMessage: e.toString(),
+        errorMessage: 'Unable to play this track. Please try another.',
+      );
+    } catch (e) {
+      // Network or other errors
+      debugPrint('Error loading track: $e');
+      state = state.copyWith(
+        isLoading: false,
+        errorMessage: 'An error occurred while loading the track.',
       );
     }
   }
@@ -110,6 +134,15 @@ class PlayerNotifier extends StateNotifier<PlayerState> {
     state = state.copyWith(isPlaying: false);
   }
 
+  /// Convenience method to toggle play/pause
+  Future<void> togglePlay() async {
+    if (state.isPlaying) {
+      await pause();
+    } else {
+      await play();
+    }
+  }
+
   Future<void> seek(Duration position) async {
     await _player.seek(position);
   }
@@ -153,6 +186,10 @@ class PlayerNotifier extends StateNotifier<PlayerState> {
 
   @override
   void dispose() {
+    // Cancel all stream subscriptions to prevent memory leaks
+    for (final subscription in _subscriptions) {
+      subscription.cancel();
+    }
     _player.dispose();
     super.dispose();
   }