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

src/server/database.js

@@ -0,0 +1,100 @@
+import Database from 'better-sqlite3';
+import { join } from 'path';
+
+class DatabaseService {
+  constructor() {
+    const dbPath = join(process.cwd(), 'data', 'settings.db');
+    this.db = new Database(dbPath);
+    this.init();
+  }
+
+  init() {
+    // Create servers table if it doesn't exist
+    this.db.exec(`
+      CREATE TABLE IF NOT EXISTS servers (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        name TEXT NOT NULL UNIQUE,
+        ip TEXT NOT NULL,
+        user TEXT NOT NULL,
+        password TEXT NOT NULL,
+        created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+        updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
+      )
+    `);
+
+    // Create trigger to update updated_at on row update
+    this.db.exec(`
+      CREATE TRIGGER IF NOT EXISTS update_servers_timestamp 
+      AFTER UPDATE ON servers
+      BEGIN
+        UPDATE servers SET updated_at = CURRENT_TIMESTAMP WHERE id = NEW.id;
+      END
+    `);
+  }
+
+  // Server CRUD operations
+  /**
+   * @param {import('../types/server').CreateServerData} serverData
+   */
+  createServer(serverData) {
+    const { name, ip, user, password } = serverData;
+    const stmt = this.db.prepare(`
+      INSERT INTO servers (name, ip, user, password) 
+      VALUES (?, ?, ?, ?)
+    `);
+    return stmt.run(name, ip, user, password);
+  }
+
+  getAllServers() {
+    const stmt = this.db.prepare('SELECT * FROM servers ORDER BY created_at DESC');
+    return stmt.all();
+  }
+
+  /**
+   * @param {number} id
+   */
+  getServerById(id) {
+    const stmt = this.db.prepare('SELECT * FROM servers WHERE id = ?');
+    return stmt.get(id);
+  }
+
+  /**
+   * @param {number} id
+   * @param {import('../types/server').CreateServerData} serverData
+   */
+  updateServer(id, serverData) {
+    const { name, ip, user, password } = serverData;
+    const stmt = this.db.prepare(`
+      UPDATE servers 
+      SET name = ?, ip = ?, user = ?, password = ?
+      WHERE id = ?
+    `);
+    return stmt.run(name, ip, user, password, id);
+  }
+
+  /**
+   * @param {number} id
+   */
+  deleteServer(id) {
+    const stmt = this.db.prepare('DELETE FROM servers WHERE id = ?');
+    return stmt.run(id);
+  }
+
+  close() {
+    this.db.close();
+  }
+}
+
+// Singleton instance
+/** @type {DatabaseService | null} */
+let dbInstance = null;
+
+export function getDatabase() {
+  if (!dbInstance) {
+    dbInstance = new DatabaseService();
+  }
+  return dbInstance;
+}
+
+export default DatabaseService;
+