Fix: Check for any existing user, not just admin role

app/database.py

@@ -80,15 +80,15 @@ async def _create_initial_admin():
         return
 
     async with AsyncSessionLocal() as session:
-        # Check if admin already exists
+        # Check if username already exists (any role)
         result = await session.execute(
-            text("SELECT id FROM agents WHERE username = :username AND role = 'admin'"),
+            text("SELECT id, role FROM agents WHERE username = :username"),
             {"username": settings.INITIAL_ADMIN_USERNAME}
         )
         existing = result.fetchone()
 
         if existing:
-            return  # Admin already exists
+            return  # Username already taken, skip creation
 
         # Create admin user with bcrypt hash
         password_hash = bcrypt.hashpw(