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/api_key.py

@@ -0,0 +1,71 @@
+"""API Key authentication dependency for FastAPI."""
+from fastapi import Depends, HTTPException, Request, status
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from src.backend.database import get_db
+from src.backend.models.orm.user import User
+
+
+async def get_current_user(
+    request: Request,
+    db: AsyncSession = Depends(get_db),
+) -> User:
+    """Extract API key from header and return the authenticated user.
+
+    The API key is sent in the X-API-Key header on every request.
+    Login endpoint is excluded from this check.
+    """
+    api_key = request.headers.get("X-API-Key")
+    if not api_key:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Missing API key in X-API-Key header",
+        )
+
+    result = await db.execute(
+        select(User).where(User.api_key == api_key, User.active == True)
+    )
+    user = result.scalar_one_or_none()
+
+    if user is None:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Invalid or inactive API key",
+        )
+
+    # Store user_id in request state for access logging middleware
+    request.state.user_id = user.id
+
+    return user
+
+
+def require_role(role: str):
+    """Dependency factory that checks if user has a specific role."""
+    async def check_role(user: User = Depends(get_current_user)) -> User:
+        if not user.has_role(role) and not user.is_admin:
+            raise HTTPException(
+                status_code=status.HTTP_403_FORBIDDEN,
+                detail=f"Role '{role}' required",
+            )
+        return user
+    return check_role
+
+
+def require_admin():
+    """Dependency that checks if user is admin."""
+    async def check_admin(user: User = Depends(get_current_user)) -> User:
+        if not user.is_admin:
+            raise HTTPException(
+                status_code=status.HTTP_403_FORBIDDEN,
+                detail="Admin access required",
+            )
+        return user
+    return check_admin
+
+
+# Pre-built role dependencies for convenience
+require_maker = require_role("Maker")
+require_measurement_tec = require_role("MeasurementTec")
+require_metrologist = require_role("Metrologist")
+require_admin_user = require_admin()