feat: add SQLite persistence and REST API for temporary whitelisting

- Migrate IP-based temporary whitelisting from file to SQLite storage
- Add REST API endpoints for managing temporary and permanent whitelists
- Create `.env.example` with required environment variables
- Document API endpoints in README.md and docs/api.md
- Add new dependency `modernc.org/sqlite` for SQLite support
- Update deployment and security documentation

cleanup.go

@@ -10,4 +10,4 @@ func cleanupLoop(db *sql.DB, interval time.Duration) {
 	for range ticker.C {
 		_ = CleanupExpiredTemp(db)
 	}
-}
+}