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>

src/types/index.ts

@@ -29,3 +29,14 @@ export interface DirectoryListing {
   path: string
   entries: FileEntry[]
 }
+
+export interface TagCategory {
+  id: string
+  name: string
+}
+
+export interface Tag {
+  id: string
+  name: string
+  categoryId: string
+}