Fix TypeScript and ESLint errors (#31)

- Add proper type annotations for WebSocketMessage and ServerInfo types
- Fix type imports to use type-only imports where appropriate
- Replace logical OR operators with nullish coalescing operators
- Fix floating promises by adding void operator
- Add proper type assertions for database results
- Fix useEffect dependencies in Terminal component
- Remove unused variables and fix unescaped entities
- Add JSDoc type annotations for database methods
- Fix singleton instance type annotations

.gitignore

@@ -14,6 +14,7 @@
 /prisma/db.sqlite
 /prisma/db.sqlite-journal
 db.sqlite
+data/settings.db
 
 # next.js
 /.next/