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/routers/stations.py

@@ -0,0 +1,142 @@
+"""Stations router - CRUD + recipe assignments."""
+from fastapi import APIRouter, Depends, HTTPException, status
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from src.backend.database import get_db
+from src.backend.api.middleware.api_key import get_current_user, require_admin_user
+from src.backend.models.orm.user import User
+from src.backend.models.api.station import (
+    StationCreate,
+    StationUpdate,
+    StationResponse,
+    StationRecipeAssignmentCreate,
+    StationRecipeAssignmentResponse,
+    RecipeSummary,
+)
+from src.backend.services import station_service
+
+router = APIRouter(prefix="/api/stations", tags=["stations"])
+
+
+@router.get("", response_model=list[StationResponse])
+async def list_stations(
+    active_only: bool = False,
+    admin: User = Depends(require_admin_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """List all stations (admin only)."""
+    stations = await station_service.list_stations(db, active_only=active_only)
+    return [StationResponse.model_validate(s) for s in stations]
+
+
+@router.post("", response_model=StationResponse, status_code=status.HTTP_201_CREATED)
+async def create_new_station(
+    data: StationCreate,
+    admin: User = Depends(require_admin_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Create a station (admin only)."""
+    station = await station_service.create_station(db, data, admin)
+    return StationResponse.model_validate(station)
+
+
+# NOTE: this literal-prefix route must stay above the /{station_id} routes.
+# The int-typed station_id param already guards against "by-code" being
+# matched as a station id, but keeping the explicit order avoids surprises
+# during refactors (e.g. if someone regroups handlers by HTTP method).
+@router.get("/by-code/{code}/recipes", response_model=list[RecipeSummary])
+async def list_recipes_by_station_code(
+    code: str,
+    user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Operator view: active recipes assigned to the station with this code.
+
+    Used by the Flask client at startup / on select_recipe page.
+    Any authenticated user can call this; filtering is by station code from
+    the client's STATION_CODE environment variable.
+    """
+    station = await station_service.get_station_by_code(db, code)
+    if station is None or not station.active:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Station not found",
+        )
+    recipes = await station_service.list_station_recipes(db, station.id)
+    return [RecipeSummary.model_validate(r) for r in recipes]
+
+
+@router.get("/{station_id}", response_model=StationResponse)
+async def get_single_station(
+    station_id: int,
+    admin: User = Depends(require_admin_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Get a station by id (admin only)."""
+    station = await station_service.get_station(db, station_id)
+    return StationResponse.model_validate(station)
+
+
+@router.put("/{station_id}", response_model=StationResponse)
+async def update_existing_station(
+    station_id: int,
+    data: StationUpdate,
+    admin: User = Depends(require_admin_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Update a station (admin only)."""
+    station = await station_service.update_station(db, station_id, data)
+    return StationResponse.model_validate(station)
+
+
+@router.delete("/{station_id}", status_code=status.HTTP_204_NO_CONTENT)
+async def remove_station(
+    station_id: int,
+    admin: User = Depends(require_admin_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Delete a station (admin only). Cascades to assignments."""
+    await station_service.delete_station(db, station_id)
+
+
+@router.get("/{station_id}/recipes", response_model=list[RecipeSummary])
+async def list_assigned_recipes(
+    station_id: int,
+    admin: User = Depends(require_admin_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Admin view: recipes assigned to this station (active only)."""
+    recipes = await station_service.list_station_recipes(db, station_id)
+    return [RecipeSummary.model_validate(r) for r in recipes]
+
+
+@router.post(
+    "/{station_id}/recipes",
+    response_model=StationRecipeAssignmentResponse,
+    status_code=status.HTTP_201_CREATED,
+)
+async def assign_recipe_to_station(
+    station_id: int,
+    data: StationRecipeAssignmentCreate,
+    admin: User = Depends(require_admin_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Assign a recipe to a station (admin only)."""
+    assignment = await station_service.assign_recipe(
+        db, station_id, data.recipe_id, admin,
+    )
+    return StationRecipeAssignmentResponse.model_validate(assignment)
+
+
+@router.delete(
+    "/{station_id}/recipes/{recipe_id}",
+    status_code=status.HTTP_204_NO_CONTENT,
+)
+async def unassign_recipe_from_station(
+    station_id: int,
+    recipe_id: int,
+    admin: User = Depends(require_admin_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Remove a recipe assignment (admin only)."""
+    await station_service.unassign_recipe(db, station_id, recipe_id)