Add file fingerprinting for move-resilient media item identity

Computes a SHA-256 partial-content fingerprint (file size + first 64 KB) for
movies, TV episodes, and mixed files during scans. When a file is moved or
renamed within a library, the scan detects the fingerprint match, renames the
media_items row in-place, and updates media_tags.media_key to match — so tags
and NFO metadata survive the move transparently.

- src/lib/fingerprint.ts: new computeFingerprint() using sync FS reads
- src/lib/db.ts: fingerprint TEXT column + index migration
- src/lib/tags.ts: reKeyMediaItem() to update media_tags on rename
- src/lib/scanner.ts: replace clear+upsert with detectMoves/reconcileAndPrune
  for movies, TV episodes, and mixed files; games retain clear+upsert (v1)
- TV scan restructured to a single filesystem pass (no double-scanning)

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

src/lib/db.ts

@@ -89,15 +89,18 @@ function initDb(db: Database.Database): void {
       genres      TEXT,
       metadata    TEXT,
       file_path   TEXT,
+      fingerprint TEXT,
       scanned_at  INTEGER NOT NULL
     );
 
     CREATE INDEX IF NOT EXISTS media_items_library_id ON media_items(library_id);
     CREATE INDEX IF NOT EXISTS media_items_parent_key ON media_items(parent_key);
+    CREATE INDEX IF NOT EXISTS media_items_fingerprint ON media_items(fingerprint);
   `)
 
   migrateLibrariesType(db)
   migrateMediaItemsSchema(db)
+  migrateMediaItemsFingerprint(db)
   seedAppSettings(db)
 }
 
@@ -162,6 +165,18 @@ function migrateMediaItemsSchema(db: Database.Database): void {
   `)
 }
 
+function migrateMediaItemsFingerprint(db: Database.Database): void {
+  const row = db
+    .prepare("SELECT sql FROM sqlite_master WHERE type='table' AND name='media_items'")
+    .get() as { sql: string } | undefined
+  if (row && !row.sql.includes('fingerprint')) {
+    db.exec(`
+      ALTER TABLE media_items ADD COLUMN fingerprint TEXT;
+      CREATE INDEX IF NOT EXISTS media_items_fingerprint ON media_items(fingerprint);
+    `)
+  }
+}
+
 function migrateLibrariesType(db: Database.Database): void {
   const row = db
     .prepare("SELECT sql FROM sqlite_master WHERE type='table' AND name='libraries'")