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/auth.py

@@ -4,8 +4,8 @@ import uuid
 from fastapi import APIRouter, HTTPException, status
 from jose import JWTError
 
-from backend.app.models.auth import LoginRequest, RefreshRequest, RegisterRequest, TokenResponse
-from backend.app.services.auth import (
+from ..models.auth import LoginRequest, RefreshRequest, RegisterRequest, TokenResponse
+from ..services.auth import (
     authenticate_user,
     create_access_token,
     create_refresh_token,
@@ -71,7 +71,7 @@ async def refresh(body: RefreshRequest) -> TokenResponse:
     new_jti = str(uuid.uuid4())
     await store_refresh_token(user_id, new_jti)
 
-    from backend.app.db import get_conn
+    from ..db import get_conn
     conn = get_conn()
     row = conn.execute(
         "SELECT email, role FROM users WHERE id = ?", [user_id]