Refactor database interactions and update footer text

- Removed community sharing and self-hosted features from the features list in page.tsx.
- Updated footer text in layout.tsx to remove the MIT License mention.
- Added @libsql/client dependency to package.json and bun.lock for database management.
- Implemented a new db.ts file to handle SQLite database connections and migrations.
- Refactored user and file management functions in users.ts and store.ts to utilize the new database client.
- Ensured legacy JSON data is imported into the new SQLite database structure on first run.

frontend/package.json

@@ -9,6 +9,7 @@
     "lint": "eslint"
   },
   "dependencies": {
+    "@libsql/client": "^0.17.3",
     "jose": "^6.2.3",
     "nanoid": "^5.1.11",
     "next": "16.2.6",