add tagging system for media items

Introduces user-defined tag categories and tags with a many-to-many
relationship to media items. Tags are stored in a SQLite database
(medialore.db via better-sqlite3) with ON DELETE CASCADE for automatic
cleanup. Users can manage categories and tags at /manage/tags, assign
tags to games in the detail modal, and tag mixed media files via a
hover button on each tile.

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

package.json

@@ -12,6 +12,8 @@
   "author": "",
   "license": "ISC",
   "dependencies": {
+    "@types/better-sqlite3": "^7.6.13",
+    "better-sqlite3": "^12.8.0",
     "next": "^15.5.14",
     "react": "^19.2.4",
     "react-dom": "^19.2.4",