fix(rate-limit): secchio login esteso a credenziali supervisore e setup (#8)

Il secchio "login" del rate limit valeva solo per /api/auth/login. Un
capoturno può ora essere attaccato a forza bruta anche via
/api/measurements/{id}/authorise e /api/production-runs/{id}/pause|
resume|close, senza mai toccare il bucket più permissivo "general".
_is_login_bucket_request confronta il path con un'espressione regolare,
non con ==, perché l'id in mezzo varia per richiesta.

Include anche la parte di #9 che riguarda questo stesso file: i path
sotto /api/setup/ entrano nello stesso secchio, indipendentemente dal
metodo (GET /api/setup/status accetta ora una password opzionale).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/backend/api/middleware/rate_limit.py

@@ -1,8 +1,10 @@
 """Rate limiting middleware for FastAPI.
 
 Implements in-memory sliding window rate limiting per client IP.
-Configurable limits for login and general endpoints.
+Configurable limits for login and endpoints that carry credentials, and for
+everything else.
 """
+import re
 import time
 from collections import defaultdict
 from typing import Callable
@@ -17,7 +19,12 @@ from src.backend.config import settings
 class RateLimitMiddleware(BaseHTTPMiddleware):
     """Middleware that enforces per-IP rate limits using a sliding window.
 
-    - Login endpoint (/api/auth/login): limited to `rate_limit_login` req/min.
+    - Login bucket: `/api/auth/login`, the paths that carry a capoturno's
+      credentials (`/api/measurements/*/authorise`,
+      `/api/production-runs/{id}/pause|resume|close`), and everything under
+      `/api/setup/` (the setup password). Limited to `rate_limit_login`
+      req/min. Guessing a supervisor's or the setup password is the same
+      attack as guessing a login password, just aimed at a different endpoint.
     - All other endpoints: limited to `rate_limit_general` req/min.
     Returns HTTP 429 with Retry-After header when limit exceeded.
 
@@ -30,6 +37,14 @@ class RateLimitMiddleware(BaseHTTPMiddleware):
     LOGIN_PATH = "/api/auth/login"
     WINDOW_SECONDS = 60
 
+    # Paths that carry a supervisor's (capoturno) credentials in the request
+    # body. Matched by pattern, not equality, because the id in the middle
+    # varies per request.
+    _SUPERVISOR_CREDENTIAL_PATTERNS = (
+        re.compile(r"^/api/measurements/\d+/authorise$"),
+        re.compile(r"^/api/production-runs/\d+/(?:pause|resume|close)$"),
+    )
+
     def __init__(self, app) -> None:
         super().__init__(app)
         # {ip: [timestamp, ...]} per bucket
@@ -70,6 +85,22 @@ class RateLimitMiddleware(BaseHTTPMiddleware):
                     return real.strip()
         return request.client.host if request.client else "unknown"
 
+    @classmethod
+    def _is_login_bucket_request(cls, method: str, path: str) -> bool:
+        """Whether this request counts against the login bucket rather than general.
+
+        `/api/setup/*` is checked regardless of method: `GET /api/setup/status`
+        now accepts an optional password (see setup.py), so guessing it there
+        is the same attack as guessing it on any of the POST endpoints.
+        """
+        if path.startswith("/api/setup/"):
+            return True
+        if method != "POST":
+            return False
+        if path == cls.LOGIN_PATH:
+            return True
+        return any(p.match(path) for p in cls._SUPERVISOR_CREDENTIAL_PATTERNS)
+
     @staticmethod
     def _effective_limit(configured: int) -> int:
         """Divide a configured per-minute limit across worker processes.
@@ -127,8 +158,9 @@ class RateLimitMiddleware(BaseHTTPMiddleware):
             self._evict_stale_ips(self._login_requests, now)
             self._evict_stale_ips(self._general_requests, now)
 
-        # Check login-specific rate limit
-        if path == self.LOGIN_PATH and request.method == "POST":
+        # Check login-bucket rate limit (login itself, supervisor-credential
+        # paths, and the setup password)
+        if self._is_login_bucket_request(request.method, path):
             allowed, retry_after = self._check_rate_limit(
                 self._login_requests, client_ip,
                 self._effective_limit(settings.rate_limit_login), now,