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/tests/test_rate_limit_proxy.py

@@ -0,0 +1,65 @@
+"""Tests for RateLimitMiddleware honoring proxy headers (X-Forwarded-For)."""
+from src.backend.api.middleware.rate_limit import RateLimitMiddleware
+
+
+class _FakeRequest:
+    """Minimal stand-in for starlette.requests.Request."""
+
+    def __init__(self, headers: dict[str, str], host: str | None = "10.0.0.1"):
+        self.headers = headers
+
+        class _Client:
+            pass
+
+        if host is None:
+            self.client = None
+        else:
+            self.client = _Client()
+            self.client.host = host
+
+
+def test_client_ip_uses_x_forwarded_for_first_hop():
+    req = _FakeRequest(
+        headers={"x-forwarded-for": "203.0.113.5, 10.0.0.2"},
+        host="10.0.0.1",
+    )
+    assert RateLimitMiddleware._client_ip(req) == "203.0.113.5"
+
+
+def test_client_ip_strips_whitespace():
+    req = _FakeRequest(headers={"x-forwarded-for": "  198.51.100.7  "})
+    assert RateLimitMiddleware._client_ip(req) == "198.51.100.7"
+
+
+def test_client_ip_falls_back_to_x_real_ip():
+    req = _FakeRequest(headers={"x-real-ip": "203.0.113.99"}, host="10.0.0.1")
+    assert RateLimitMiddleware._client_ip(req) == "203.0.113.99"
+
+
+def test_client_ip_falls_back_to_request_client_host():
+    req = _FakeRequest(headers={}, host="172.18.0.5")
+    assert RateLimitMiddleware._client_ip(req) == "172.18.0.5"
+
+
+def test_client_ip_returns_unknown_without_client():
+    req = _FakeRequest(headers={}, host=None)
+    assert RateLimitMiddleware._client_ip(req) == "unknown"
+
+
+def test_x_forwarded_for_overrides_x_real_ip():
+    req = _FakeRequest(
+        headers={
+            "x-forwarded-for": "203.0.113.5",
+            "x-real-ip": "10.0.0.2",
+        },
+        host="10.0.0.1",
+    )
+    assert RateLimitMiddleware._client_ip(req) == "203.0.113.5"
+
+
+def test_empty_x_forwarded_for_falls_through():
+    req = _FakeRequest(
+        headers={"x-forwarded-for": "", "x-real-ip": "203.0.113.42"},
+        host="10.0.0.1",
+    )
+    assert RateLimitMiddleware._client_ip(req) == "203.0.113.42"