Fix media_tags not updating when fingerprint move is detected

reKeyMediaItem was called with item_key values (e.g. "lib1:movie:Inception")
but media_tags stores keys in the shorter UI format (e.g. "lib1:Inception"),
so the UPDATE never matched any rows.

Add itemKeyToMediaKey() to extract the terminal segment of an item_key and
reconstruct the media_key format the UI uses:
  lib1:movie:Inception%20(2010)          → lib1:Inception%20(2010)
  lib1:tv_episode:Show:Season1:ep.mkv   → lib1:ep.mkv
  lib1:mixed_file:dir%2Ffile.mp4        → lib1:dir%2Ffile.mp4

Also skip the UPDATE when old and new media_keys are identical (e.g. a TV
episode moved between seasons keeps the same filename-based media_key).

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

src/lib/scanner.ts

@@ -531,6 +531,22 @@ function detectMoves(
  * Tags on deleted items are intentionally left as orphans — harmless and
  * recoverable if the file reappears.
  */
+/**
+ * Converts an item_key (used in media_items) to the media_key format used in
+ * media_tags. The UI constructs media_keys as `${libraryId}:${shortId}` where
+ * shortId is only the terminal path segment — e.g.:
+ *   "lib1:movie:Inception%20(2010)"     → "lib1:Inception%20(2010)"
+ *   "lib1:tv_episode:Show:S1:ep.mkv"   → "lib1:ep.mkv"
+ *   "lib1:mixed_file:dir%2Ffile.mp4"   → "lib1:dir%2Ffile.mp4"
+ */
+function itemKeyToMediaKey(itemKey: string): string {
+  const firstColon = itemKey.indexOf(':')
+  const lastColon = itemKey.lastIndexOf(':')
+  const libraryId = itemKey.slice(0, firstColon)
+  const shortId = itemKey.slice(lastColon + 1)
+  return `${libraryId}:${shortId}`
+}
+
 function reconcileAndPrune(
   db: Database.Database,
   libraryId: string,
@@ -541,7 +557,12 @@ function reconcileAndPrune(
 
   for (const { oldKey, newKey } of moves) {
     renameItem.run(newKey, oldKey)
-    reKeyMediaItem(oldKey, newKey)
+    // Convert item_keys to the media_key format actually used in media_tags
+    const oldMediaKey = itemKeyToMediaKey(oldKey)
+    const newMediaKey = itemKeyToMediaKey(newKey)
+    if (oldMediaKey !== newMediaKey) {
+      reKeyMediaItem(oldMediaKey, newMediaKey)
+    }
     console.log(`[scanner]   fingerprint match: renamed "${oldKey}" → "${newKey}"`)
   }