Add multi-platform game support with per-OS download detection

- Detect Windows (.zip), Linux (.tar.gz), and macOS (.dmg / .app bundle) game archives during scan
- Store GameFile[] with platform metadata in DB instead of plain zipFiles[]
- Stream .app bundles as on-the-fly zip archives via archiver
- Show WIN/LIN/MAC platform badge pills on GameCard and SeriesCard
- Auto-select the download matching the user's OS in GameDetailModal
- Persist cover URL to DB immediately on upload (no re-scan needed)
- Backward-compatible: legacy zipFiles entries map to platform 'windows'

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/scanner.ts

@@ -391,7 +391,7 @@ async function scanGames(library: Library, libraryRoot: string): Promise<void> {
           parent_key: seriesKey,
           title: game.title,
           metadata: JSON.stringify({
-            zipFiles: game.zipFiles,
+            gameFiles: game.gameFiles,
             coverUrl: game.coverUrl,
             wideCoverUrl: game.wideCoverUrl,
           }),
@@ -414,7 +414,7 @@ async function scanGames(library: Library, libraryRoot: string): Promise<void> {
         item_type: 'game',
         title: game.title,
         metadata: JSON.stringify({
-          zipFiles: game.zipFiles,
+          gameFiles: game.gameFiles,
           coverUrl: game.coverUrl,
           wideCoverUrl: game.wideCoverUrl,
         }),