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/app/layout.tsx

@@ -197,7 +197,7 @@ export default async function RootLayout({
             </div>
 
             <div className="mt-12 pt-8 border-t border-white/5 flex flex-wrap items-center justify-between gap-4 text-xs text-slate-600">
-              <p>© {new Date().getFullYear()} Backerup — Open source under the MIT License.</p>
+              <p>© {new Date().getFullYear()} Backerup — Open source.</p>
               <div className="flex items-center gap-2">
                 <span className="w-1.5 h-1.5 rounded-full bg-emerald-500 animate-pulse" />
                 <span>All systems operational</span>