feat(hardening): login rate limiting, per-service memory limits, pinned images

- slowapi limiter on POST /auth/login (10/min per IP, Persian error msg);
  edge-level coarse limits stay in Traefik
- mem_limit on every main-compose service (~4.4GB worst case, protects the
  8GB shared host during rebuilds)
- monitoring images pinned to verified tags (prom v3.4.1, grafana 11.6.3,
  loki/promtail 3.5.0, node-exporter v1.9.1, postgres-exporter v0.17.1,
  cadvisor v0.49.1); exporter image name fixed to postgres-exporter

backend/app/main.py

@@ -16,6 +16,8 @@ from fastapi.exceptions import RequestValidationError
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import JSONResponse
 from prometheus_fastapi_instrumentator import Instrumentator
+from slowapi import _rate_limit_exceeded_handler
+from slowapi.errors import RateLimitExceeded
 from sqlalchemy import text as sql_text
 from sqlalchemy.exc import IntegrityError
 
@@ -34,6 +36,7 @@ from app.observability import RequestContextMiddleware, setup_logging
 from app.routers import ROUTERS
 from app.services.quote_service import auto_expire_quotes
 from app.utils.errors import AppError
+from app.utils.ratelimit import limiter
 
 setup_logging(settings.LOG_FORMAT)
 logger = logging.getLogger("procurement")
@@ -131,6 +134,10 @@ app.add_middleware(
 )
 app.add_middleware(RequestContextMiddleware)
 
+# Rate limiting — login brute-force brake (edge rate limit lives in Traefik).
+app.state.limiter = limiter
+app.add_exception_handler(RateLimitExceeded, _rate_limit_exceeded_handler)
+
 # Prometheus /metrics (requests, latency, errors) — mounted at app level,
 # outside the authenticated /api/v1 prefix; scrape target for the
 # monitoring stack.

backend/app/routers/auth.py

@@ -13,7 +13,7 @@ Error mapping (documented in docs/casdoor-auth.md):
 import logging
 
 import httpx
-from fastapi import APIRouter, Depends
+from fastapi import APIRouter, Depends, Request
 from pydantic import BaseModel
 from sqlalchemy.ext.asyncio import AsyncSession
 
@@ -23,6 +23,7 @@ from app.db.engine import get_db
 from app.routers.users import _user_projects, user_to_dict
 from app.services import analytics
 from app.utils.errors import ServiceUnavailableError, UnauthorizedError
+from app.utils.ratelimit import limiter
 
 logger = logging.getLogger("procurement.auth")
 
@@ -35,7 +36,8 @@ class LoginRequest(BaseModel):
 
 
 @router.post("/login")
-async def login(payload: LoginRequest, db: AsyncSession = Depends(get_db)):
+@limiter.limit("10/minute", error_message="تلاش‌های ورود بیش از حد مجاز — کمی بعد دوباره امتحان کنید")
+async def login(request: Request, payload: LoginRequest, db: AsyncSession = Depends(get_db)):
     """Exchange username/password for a Casdoor JWT (OAuth password grant)."""
     url = f"{settings.CASDOOR_ENDPOINT}/api/login/oauth/access_token"
     form = {

backend/app/utils/ratelimit.py

@@ -0,0 +1,11 @@
+"""Shared rate limiter (slowapi) — in-memory, single-worker friendly.
+
+Login brute-force brake: the edge (Traefik) has a coarse per-IP limit for
+the whole API host; this adds a tight limit on the credential endpoint
+itself. Kept in its own module so routers can import it without a circular
+import on app.main.
+"""
+from slowapi import Limiter
+from slowapi.util import get_remote_address
+
+limiter = Limiter(key_func=get_remote_address)