chore(v2): restructure monorepo to src/ layout with uv

Aligns the repo with the python-project-spec-design.md template chosen
for V2.0.0. Big move, no logic changes. The 3 pre-existing test
failures (test_recipes::test_update_recipe, test_recipes::
test_recipe_versioning, test_tasks::test_reorder_tasks, plus the
client test_save_measurement_proxy) survive unchanged.

Layout changes
- server/        -> src/backend/
- server/middleware/ -> src/backend/api/middleware/
- server/routers/    -> src/backend/api/routers/
- server/models/     -> src/backend/models/orm/
- server/schemas/    -> src/backend/models/api/
- server/uploads/    -> uploads/ (project root, mounted volume)
- server/tests/      -> src/backend/tests/
- client/            -> src/frontend/flask_app/ (Flask kept; React
  deroga is documented in CLAUDE.md, justified by tablet UX, USB
  caliper/barcode workflow and Fabric.js integration)

Tooling
- pyproject.toml: monorepo with [project] core deps and
  optional-dependencies server / client / dev. Replaces both
  server/requirements.txt and client/requirements.txt.
- uv.lock + .python-version (3.11) committed for reproducible builds.
- Dockerfile (root, backend) and Dockerfile.frontend rewritten to use
  uv sync --frozen --no-dev --extra server|client; legacy Dockerfiles
  preserved as Dockerfile.legacy for reference but excluded from build
  context via .dockerignore.
- docker-compose.dev.yml + docker-compose.yml: build context now ".",
  dockerfile pointing to the root files.

Code adjustments forced by the move
- Every "from config|database|models|schemas|services|routers|middleware
  import ..." rewritten to its src.backend.* equivalent (50+ files
  including indented inline imports inside test bodies).
- src/backend/migrations/env.py: insert project root into sys.path so
  alembic can resolve src.backend.* imports regardless of cwd.
- src/backend/config.py: env_file ../../.env (was ../.env), upload_path
  resolves project root via parents[2].
- src/backend/tests/conftest.py + tests: import ... from src.backend.*
  instead of bare names; old per-directory pytest.ini files removed in
  favor of root pyproject.toml [tool.pytest.ini_options].
- .gitignore: uploads/ at root, src/frontend/flask_app/static/css/
  tailwind.css path; .dockerignore tightened.
- CLAUDE.md: rewrote sections "Layout del repository", "Comandi di
  Sviluppo", "Database & Migrations", "Test", "i18n", and all path
  references throughout the architecture sections.

Verified
- uv lock resolves 77 packages; uv sync --extra server --extra client
  --extra dev installs cleanly.
- uv run pytest: 171 passed, 4 pre-existing failures.
- uv run alembic -c src/backend/migrations/alembic.ini check loads
  config and metadata (errors only on the absent local MySQL).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/backend/api/middleware/rate_limit.py

@@ -0,0 +1,123 @@
+"""Rate limiting middleware for FastAPI.
+
+Implements in-memory sliding window rate limiting per client IP.
+Configurable limits for login and general endpoints.
+"""
+import time
+from collections import defaultdict
+from typing import Callable
+
+from fastapi import Request, Response
+from starlette.middleware.base import BaseHTTPMiddleware
+from starlette.responses import JSONResponse
+
+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.
+    - All other endpoints: limited to `rate_limit_general` req/min.
+    Returns HTTP 429 with Retry-After header when limit exceeded.
+    """
+
+    LOGIN_PATH = "/api/auth/login"
+    WINDOW_SECONDS = 60
+
+    def __init__(self, app) -> None:
+        super().__init__(app)
+        # {ip: [timestamp, ...]} per bucket
+        self._login_requests: dict[str, list[float]] = defaultdict(list)
+        self._general_requests: dict[str, list[float]] = defaultdict(list)
+        self._request_count = 0  # Counter for triggering eviction
+
+    @staticmethod
+    def _client_ip(request: Request) -> str:
+        """Resolve the originating client IP, honoring proxy headers.
+
+        Order of precedence: ``X-Forwarded-For`` (first hop), ``X-Real-IP``,
+        ``request.client.host``. Required because Nginx and the Flask client
+        sit between the tablet and the API; without parsing these headers
+        every tablet shares one bucket.
+        """
+        xff = request.headers.get("x-forwarded-for")
+        if xff:
+            first = xff.split(",")[0].strip()
+            if first:
+                return first
+        real = request.headers.get("x-real-ip")
+        if real:
+            return real.strip()
+        return request.client.host if request.client else "unknown"
+
+    def _clean_window(self, timestamps: list[float], now: float) -> list[float]:
+        """Remove timestamps outside the current sliding window."""
+        cutoff = now - self.WINDOW_SECONDS
+        return [t for t in timestamps if t > cutoff]
+
+    def _evict_stale_ips(self, bucket: dict[str, list[float]], now: float) -> None:
+        """Remove IP entries with no timestamps in the current window (memory leak prevention)."""
+        cutoff = now - self.WINDOW_SECONDS
+        stale_ips = [ip for ip, timestamps in bucket.items() if not timestamps or max(timestamps) <= cutoff]
+        for ip in stale_ips:
+            del bucket[ip]
+
+    def _check_rate_limit(
+        self,
+        bucket: dict[str, list[float]],
+        client_ip: str,
+        limit: int,
+        now: float,
+    ) -> tuple[bool, int]:
+        """Check if a request is within the rate limit.
+
+        Returns:
+            Tuple of (allowed, retry_after_seconds).
+        """
+        bucket[client_ip] = self._clean_window(bucket[client_ip], now)
+
+        if len(bucket[client_ip]) >= limit:
+            # Calculate seconds until the oldest request falls out of window
+            oldest = bucket[client_ip][0]
+            retry_after = int(oldest + self.WINDOW_SECONDS - now) + 1
+            return False, max(retry_after, 1)
+
+        bucket[client_ip].append(now)
+        return True, 0
+
+    async def dispatch(self, request: Request, call_next: Callable) -> Response:
+        client_ip = self._client_ip(request)
+        now = time.time()
+        path = request.url.path
+
+        # Periodic eviction: every 100 requests, remove stale IP buckets
+        self._request_count += 1
+        if self._request_count % 100 == 0:
+            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":
+            allowed, retry_after = self._check_rate_limit(
+                self._login_requests, client_ip, settings.rate_limit_login, now
+            )
+            if not allowed:
+                return JSONResponse(
+                    status_code=429,
+                    content={"detail": "Too many login attempts. Please try again later."},
+                    headers={"Retry-After": str(retry_after)},
+                )
+
+        # Check general rate limit
+        allowed, retry_after = self._check_rate_limit(
+            self._general_requests, client_ip, settings.rate_limit_general, now
+        )
+        if not allowed:
+            return JSONResponse(
+                status_code=429,
+                content={"detail": "Too many requests. Please try again later."},
+                headers={"Retry-After": str(retry_after)},
+            )
+
+        return await call_next(request)