Go back to the hardlink deduplicator (1da0132), keeping backups

Restores the code of 1da0132 ("Add a setting to hide the quarantine from
Plex") and removes everything added after it: the tag editor, album art,
organizing/naming, the step-by-step tune-up and library types.

Kept:
- Database backups (Settings -> Backups): scheduled, manual, download,
  restore, and the optional backup before every action.
- The .env-driven docker-compose.yml for Arcane.

Databases that already ran the later migrations keep working: migrations
6-10 stay in the list (they only add columns) so numbering never goes
backwards, and Undo refuses History entries of removed features instead
of treating them as links.

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

internal/store/store.go

@@ -119,6 +119,10 @@ var migrations = []string{
 	// undo must then leave that target alone.
 	`ALTER TABLE operations ADD COLUMN link_preexisted INTEGER NOT NULL DEFAULT 0;`,
 
+	// 6-10 belong to features that were removed again (tag editing,
+	// organizing, the step-by-step fixer). They only add columns, which are
+	// unused now, and stay so databases that already ran them keep the same
+	// numbering and future migrations are never skipped.
 	// 6: operation-specific details as JSON (e.g. which tags an edit changed).
 	`ALTER TABLE operations ADD COLUMN detail TEXT NOT NULL DEFAULT '';`,