Refactor import statements across multiple modules to use relative paths for better organization and maintainability.

Co-authored-by: Copilot <copilot@github.com>

backend/app/routers/admin.py

@@ -3,8 +3,8 @@ from datetime import datetime, timezone
 
 from fastapi import APIRouter, Depends
 
-from backend.app.db import get_conn, get_write_lock
-from backend.app.dependencies import require_admin
+from ..db import get_conn, get_write_lock
+from ..dependencies import require_admin
 
 router = APIRouter(prefix="/admin", tags=["admin"])