feat: implement admin dashboard with site settings, user management, and activity monitoring

backend/src/db/migrations.ts

@@ -7,6 +7,7 @@ export function runMigrations(db: Database.Database): void {
       email          TEXT UNIQUE NOT NULL,
       password_hash  TEXT NOT NULL,
       display_name   TEXT NOT NULL,
+      role           TEXT NOT NULL DEFAULT 'user',
       email_verified INTEGER DEFAULT 0,
       verify_token   TEXT,
       verify_expires INTEGER,
@@ -42,7 +43,43 @@ export function runMigrations(db: Database.Database): void {
       completed_at  INTEGER DEFAULT (unixepoch())
     );
 
+    CREATE TABLE IF NOT EXISTS site_settings (
+      key        TEXT PRIMARY KEY,
+      value      TEXT NOT NULL,
+      updated_at INTEGER DEFAULT (unixepoch())
+    );
+
     CREATE INDEX IF NOT EXISTS idx_saved_exams_user ON saved_exams(user_id);
     CREATE INDEX IF NOT EXISTS idx_exam_results_user ON exam_results(user_id);
   `)
+
+  // ── Add role column if missing (existing databases) ──
+  const cols = db.prepare(`PRAGMA table_info(users)`).all() as { name: string }[]
+  if (!cols.some(c => c.name === 'role')) {
+    db.exec(`ALTER TABLE users ADD COLUMN role TEXT NOT NULL DEFAULT 'user'`)
+  }
+
+  // ── Promote first user to admin if no admins exist ──
+  const adminCount = db.prepare(`SELECT COUNT(*) AS cnt FROM users WHERE role = 'admin'`).get() as { cnt: number }
+  if (adminCount.cnt === 0) {
+    db.prepare(`UPDATE users SET role = 'admin' WHERE id = (SELECT MIN(id) FROM users)`).run()
+  }
+
+  // ── Seed default settings ──
+  const defaults: Record<string, string> = {
+    site_name: 'BrainWave',
+    max_upload_mb: '5',
+    allow_guest_mode: 'true',
+    registration_enabled: 'true',
+    default_theme: 'light',
+    maintenance_mode: 'false',
+    maintenance_message: 'We are currently performing maintenance. Please check back soon.',
+  }
+  const upsert = db.prepare(`
+    INSERT INTO site_settings (key, value) VALUES (?, ?)
+    ON CONFLICT(key) DO NOTHING
+  `)
+  for (const [key, value] of Object.entries(defaults)) {
+    upsert.run(key, value)
+  }
 }