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/frontend/flask_app/tests/test_auth.py

@@ -0,0 +1,130 @@
+"""Tests for auth blueprint (client/blueprints/auth.py).
+
+Covers login GET/POST, logout, unauthenticated redirect, and language/theme switch.
+"""
+import pytest
+from unittest.mock import patch
+
+
+class TestLoginPage:
+    """GET /auth/login tests."""
+
+    def test_login_page_renders(self, client):
+        """Login page renders successfully with 200 status."""
+        resp = client.get("/auth/login")
+        assert resp.status_code == 200
+        assert b"login" in resp.data.lower() or b"Login" in resp.data
+
+    def test_login_page_redirects_when_already_logged_in(self, logged_in_client):
+        """Already authenticated user is redirected away from login."""
+        resp = logged_in_client.get("/auth/login")
+        assert resp.status_code == 302
+
+
+class TestLoginPost:
+    """POST /auth/login tests."""
+
+    def test_login_post_success_redirects(self, client, mock_api_client):
+        """Successful login POST sets session and redirects."""
+        mock_api_client.post.return_value = {
+            "api_key": "new-api-key-abc",
+            "user": {
+                "id": 1,
+                "username": "testuser",
+                "display_name": "Test User",
+                "roles": ["MeasurementTec"],
+                "is_admin": False,
+                "language_pref": "en",
+                "theme_pref": "light",
+                "active": True,
+            },
+        }
+        # Mock settings call made after login
+        mock_api_client.get.return_value = {}
+
+        resp = client.post(
+            "/auth/login",
+            data={"username": "testuser", "password": "pass123"},
+            follow_redirects=False,
+        )
+        assert resp.status_code == 302
+        mock_api_client.post.assert_called_once()
+
+        # Verify session was populated
+        with client.session_transaction() as sess:
+            assert sess.get("api_key") == "new-api-key-abc"
+            assert sess["user"]["username"] == "testuser"
+
+    def test_login_post_error_shows_error(self, client, mock_api_client):
+        """Failed login returns the login page with error flash."""
+        mock_api_client.post.return_value = {
+            "error": True,
+            "detail": "Credenziali non valide",
+        }
+
+        resp = client.post(
+            "/auth/login",
+            data={"username": "bad", "password": "wrong"},
+            follow_redirects=True,
+        )
+        assert resp.status_code == 200
+        # Error message should appear in the response (flashed)
+        assert b"Credenziali non valide" in resp.data or b"login" in resp.data.lower()
+
+    def test_login_post_empty_fields(self, client, mock_api_client):
+        """Login with empty username/password shows validation error."""
+        resp = client.post(
+            "/auth/login",
+            data={"username": "", "password": ""},
+            follow_redirects=True,
+        )
+        assert resp.status_code == 200
+        # Should render login again (not crash)
+
+
+class TestLogout:
+    """GET/POST /auth/logout tests."""
+
+    def test_logout_clears_session(self, logged_in_client, mock_api_client):
+        """Logout clears session and redirects to login."""
+        mock_api_client.post.return_value = {}
+
+        resp = logged_in_client.get("/auth/logout", follow_redirects=False)
+        assert resp.status_code == 302
+        assert "/auth/login" in resp.headers["Location"]
+
+        # Session should be cleared
+        with logged_in_client.session_transaction() as sess:
+            assert "api_key" not in sess
+            assert "user" not in sess
+
+
+class TestUnauthenticatedRedirect:
+    """Protected routes redirect unauthenticated users."""
+
+    def test_profile_requires_login(self, client):
+        """Profile page redirects to login when not authenticated."""
+        resp = client.get("/auth/profile", follow_redirects=False)
+        assert resp.status_code == 302
+        assert "/auth/login" in resp.headers["Location"]
+
+
+class TestLanguageSwitch:
+    """Language and theme switching via app routes."""
+
+    def test_set_language_stores_in_session(self, client):
+        """Setting language updates session and redirects back."""
+        resp = client.get("/set-language/en", follow_redirects=False)
+        assert resp.status_code == 302
+
+        with client.session_transaction() as sess:
+            assert sess.get("language") == "en"
+
+    def test_set_language_invalid_ignored(self, client):
+        """Setting an unsupported language does not crash and still redirects."""
+        resp = client.get("/set-language/xx", follow_redirects=False)
+        assert resp.status_code == 302
+
+        with client.session_transaction() as sess:
+            # Invalid language should NOT be stored
+            assert sess.get("language") != "xx"