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_station_model.py

@@ -0,0 +1,73 @@
+"""Test the Station and StationRecipeAssignment ORM models."""
+import pytest
+from sqlalchemy import select
+from sqlalchemy.exc import IntegrityError
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from src.backend.models.orm.station import Station, StationRecipeAssignment
+from src.backend.tests.conftest import _create_user, create_test_recipe
+
+
+async def test_create_station(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="admin1", is_admin=True)
+    station = Station(
+        code="ST-001",
+        name="Linea 1",
+        location="Reparto Nord",
+        created_by=admin.id,
+    )
+    db_session.add(station)
+    await db_session.flush()
+    await db_session.refresh(station)
+    assert station.id is not None
+    assert station.active is True
+    assert station.created_at is not None
+
+
+async def test_station_code_is_unique(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="admin2", is_admin=True)
+    db_session.add(Station(code="ST-DUP", name="A", created_by=admin.id))
+    await db_session.flush()
+    db_session.add(Station(code="ST-DUP", name="B", created_by=admin.id))
+    with pytest.raises(IntegrityError):
+        await db_session.flush()
+    await db_session.rollback()
+
+
+async def test_assign_recipe_to_station(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="admin3", is_admin=True)
+    station = Station(code="ST-002", name="Linea 2", created_by=admin.id)
+    db_session.add(station)
+    await db_session.flush()
+    recipe = await create_test_recipe(db_session, user_id=admin.id, code="REC-X")
+    assignment = StationRecipeAssignment(
+        station_id=station.id, recipe_id=recipe.id, assigned_by=admin.id,
+    )
+    db_session.add(assignment)
+    await db_session.flush()
+    result = await db_session.execute(
+        select(StationRecipeAssignment).where(
+            StationRecipeAssignment.station_id == station.id
+        )
+    )
+    assignments = result.scalars().all()
+    assert len(assignments) == 1
+    assert assignments[0].recipe_id == recipe.id
+
+
+async def test_duplicate_assignment_is_rejected(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="admin4", is_admin=True)
+    station = Station(code="ST-003", name="Linea 3", created_by=admin.id)
+    db_session.add(station)
+    await db_session.flush()
+    recipe = await create_test_recipe(db_session, user_id=admin.id, code="REC-Y")
+    db_session.add(StationRecipeAssignment(
+        station_id=station.id, recipe_id=recipe.id, assigned_by=admin.id,
+    ))
+    await db_session.flush()
+    db_session.add(StationRecipeAssignment(
+        station_id=station.id, recipe_id=recipe.id, assigned_by=admin.id,
+    ))
+    with pytest.raises(IntegrityError):
+        await db_session.flush()
+    await db_session.rollback()