perf(database): skip the per-launch duplicate scan and keep playlist payloads last (#1883)

deduplicateXtreamCache no longer scans the whole catalog on every launch once both unique indexes exist (7.8 s cold on a 3.9M-title library). The playlists table keeps payload as its last column (playlists-table.ts); ensurePlaylistsPayloadLast rebuilds an existing table once, keeping its indexes and triggers, foreign keys off, committing only if references referencing playlists gain no violations. On a full copy of that profile initDatabase went from 5.2-8.1 s to 39 ms and the playlist metadata read from 1.5-2 s to 22-34 ms; the one-time rebuild costs about 4 s.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.changes/database-startup-scans.md

@@ -0,0 +1,6 @@
+---
+type: perf
+area: database
+---
+
+The app starts faster on large libraries: the catalog is no longer scanned for duplicates on every launch, and reading the playlist list no longer walks every M3U playlist's channel data (a one-time rebuild of the playlists table on the first start after the update).