Add admin account with user management endpoints

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/dependencies.py

@@ -31,5 +31,13 @@ async def get_current_user(
     user = result.scalar_one_or_none()
     if user is None:
         raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="User not found")
+    if user.is_disabled:
+        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Account disabled")
 
     return user
+
+
+async def get_current_admin(current_user=Depends(get_current_user)):
+    if not current_user.is_admin:
+        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Admin access required")
+    return current_user