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_auth.py

@@ -0,0 +1,96 @@
+"""Tests for authentication router (/api/auth)."""
+import pytest
+from httpx import AsyncClient
+
+from src.backend.tests.conftest import _create_user, auth_headers
+
+
+class TestLogin:
+    """POST /api/auth/login tests."""
+
+    async def test_login_success(self, client: AsyncClient, db_session):
+        """Successful login returns user data and API key."""
+        user = await _create_user(
+            db_session, username="loginuser", password="SecurePass1"
+        )
+        resp = await client.post(
+            "/api/auth/login",
+            json={"username": "loginuser", "password": "SecurePass1"},
+        )
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["user"]["username"] == "loginuser"
+        assert "api_key" in data
+        assert len(data["api_key"]) > 0
+
+    async def test_login_wrong_password(self, client: AsyncClient, db_session):
+        """Login with wrong password returns 401."""
+        await _create_user(
+            db_session, username="wrongpw", password="CorrectPass1"
+        )
+        resp = await client.post(
+            "/api/auth/login",
+            json={"username": "wrongpw", "password": "WrongPass1"},
+        )
+        assert resp.status_code == 401
+        assert "Invalid" in resp.json()["detail"]
+
+    async def test_login_unknown_user(self, client: AsyncClient):
+        """Login with non-existent username returns 401."""
+        resp = await client.post(
+            "/api/auth/login",
+            json={"username": "nonexistent", "password": "Anything1"},
+        )
+        assert resp.status_code == 401
+
+    async def test_login_inactive_user(self, client: AsyncClient, db_session):
+        """Login with inactive user returns 401."""
+        await _create_user(
+            db_session,
+            username="inactive_user",
+            password="InactivePass1",
+            active=False,
+        )
+        resp = await client.post(
+            "/api/auth/login",
+            json={"username": "inactive_user", "password": "InactivePass1"},
+        )
+        assert resp.status_code == 401
+
+    async def test_login_missing_fields(self, client: AsyncClient):
+        """Login with missing fields returns 422."""
+        resp = await client.post("/api/auth/login", json={"username": "only"})
+        assert resp.status_code == 422
+
+    async def test_login_returns_api_key(self, client: AsyncClient, db_session):
+        """Login response contains a valid api_key string."""
+        await _create_user(
+            db_session, username="apikey_user", password="KeyPass123"
+        )
+        resp = await client.post(
+            "/api/auth/login",
+            json={"username": "apikey_user", "password": "KeyPass123"},
+        )
+        assert resp.status_code == 200
+        api_key = resp.json()["api_key"]
+        # API key should be a non-empty string (base64url, ~64 chars)
+        assert isinstance(api_key, str)
+        assert len(api_key) >= 32
+
+
+class TestHealthAndAuth:
+    """Health check and auth requirement tests."""
+
+    async def test_health_check_no_auth(self, client: AsyncClient):
+        """Health check endpoint works without authentication."""
+        resp = await client.get("/api/health")
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["status"] == "ok"
+        assert "version" in data
+
+    async def test_endpoint_requires_api_key(self, client: AsyncClient):
+        """Protected endpoint returns 401 without API key."""
+        resp = await client.get("/api/users")
+        assert resp.status_code == 401
+        assert "API key" in resp.json()["detail"] or "Missing" in resp.json()["detail"]