feat: add danmaku replay player integration

- Add IDanmakuService interface and DanmakuService implementation to parse danmaku XML files
- Add GET /api/record-tasks/{id}/danmaku and GET /api/record-sessions/{id}/danmaku endpoints
- Add DanmakuPlayer Vue component with native video + CSS overlay danmaku rendering
- Add danmakuEngine.ts pure-TypeScript animation loop with binary search, track management, and event notifications
- Add useDanmakuPlayer composable for reusable danmaku data loading
- Integrate danmaku toggle button into RecordTaskDetailView
- Integrate danmaku replay modal dialog into RecordSessionDetailView segment table

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/LiveRecorder.WebApi/Program.cs

@@ -183,6 +183,7 @@ builder.Services.AddScoped<StoppedOrphanRecordSessionCleanupService>();
 builder.Services.AddScoped<PlatformHttpClientFactory>();
 builder.Services.AddScoped<PlatformHttpRequestService>();
 builder.Services.AddScoped<RecordUploadService>();
+builder.Services.AddScoped<IDanmakuService, DanmakuService>();
 builder.Services.AddScoped<DatabaseInitializer>();
 builder.Services.AddScoped<SqliteToPostgresMigrationService>();