feat: Windows support - auto-update system + proper app icon

- PowerShell silent installer with UAC elevation
- Smart asset detection (x64 priority for .exe)
- Cross-platform restart after update
- Auto-check updates on launch (5 sec delay)
- Multi-layer .ico with 6 sizes (16-256px)
- Windows build documentation added

lib/features/app_update/model/remote_version_entity.dart

@@ -18,12 +18,73 @@ class RemoteVersionEntity with _$RemoteVersionEntity {
     @Default([]) List<ReleaseAsset> assets,
   }) = _RemoteVersionEntity;
 
-  String get presentVersion =>
-      flavor == Environment.prod ? version : "$version ${flavor.name}";
+  String get presentVersion => flavor == Environment.prod ? version : "$version ${flavor.name}";
 
-  /// Найти asset по расширению файла
+  /// Найти asset по расширению файла с умным определением
   String? findAssetByExtension(String extension) {
     try {
+      // Для Linux используем приоритет: .deb > .rpm > .AppImage
+      if (extension == '.deb' || extension == '.rpm' || extension == '.AppImage') {
+        final priorities = ['.deb', '.rpm', '.AppImage'];
+
+        for (final ext in priorities) {
+          try {
+            final asset = assets.firstWhere((asset) => asset.name.endsWith(ext));
+            return asset.downloadUrl;
+          } catch (_) {
+            continue;
+          }
+        }
+        return null;
+      }
+
+      // Для Windows - ищем .exe с приоритетом x64
+      if (extension == '.exe') {
+        // Сначала ищем x64 setup/installer
+        for (final pattern in ['x64', 'amd64', 'win64', 'setup', 'installer']) {
+          try {
+            final asset = assets.firstWhere(
+              (asset) => asset.name.toLowerCase().contains(pattern) && asset.name.endsWith('.exe'),
+            );
+            return asset.downloadUrl;
+          } catch (_) {
+            continue;
+          }
+        }
+        
+        // Если не нашли специфичный - берём любой .exe
+        try {
+          final asset = assets.firstWhere((asset) => asset.name.endsWith('.exe'));
+          return asset.downloadUrl;
+        } catch (_) {
+          return null;
+        }
+      }
+
+      // Для macOS - ищем .dmg
+      if (extension == '.dmg') {
+        // Сначала ищем universal или arm64 (для M1/M2)
+        for (final pattern in ['universal', 'arm64', 'apple-silicon']) {
+          try {
+            final asset = assets.firstWhere(
+              (asset) => asset.name.toLowerCase().contains(pattern) && asset.name.endsWith('.dmg'),
+            );
+            return asset.downloadUrl;
+          } catch (_) {
+            continue;
+          }
+        }
+        
+        // Если не нашли - берём любой .dmg
+        try {
+          final asset = assets.firstWhere((asset) => asset.name.endsWith('.dmg'));
+          return asset.downloadUrl;
+        } catch (_) {
+          return null;
+        }
+      }
+
+      // Для других расширений - прямой поиск
       return assets.firstWhere((asset) => asset.name.endsWith(extension)).downloadUrl;
     } catch (_) {
       return null;