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_settings.py

@@ -0,0 +1,107 @@
+"""Tests for settings router (/api/settings)."""
+import pytest
+from httpx import AsyncClient
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from src.backend.models.orm.setting import SystemSetting
+from src.backend.models.orm.user import User
+from src.backend.tests.conftest import auth_headers
+
+
+class TestGetSettings:
+    """GET /api/settings/ tests."""
+
+    async def test_get_settings(
+        self,
+        client: AsyncClient,
+        admin_user: User,
+        db_session: AsyncSession,
+    ):
+        """Authenticated user can retrieve settings."""
+        # Seed a setting
+        setting = SystemSetting(
+            setting_key="test_setting",
+            setting_value="test_value",
+            setting_type="string",
+        )
+        db_session.add(setting)
+        await db_session.flush()
+
+        resp = await client.get(
+            "/api/settings/", headers=auth_headers(admin_user)
+        )
+        assert resp.status_code == 200
+        data = resp.json()
+        assert isinstance(data, dict)
+        assert data.get("test_setting") == "test_value"
+
+    async def test_get_settings_empty(
+        self, client: AsyncClient, maker_user: User
+    ):
+        """Empty settings returns empty dict."""
+        resp = await client.get(
+            "/api/settings/", headers=auth_headers(maker_user)
+        )
+        assert resp.status_code == 200
+        assert resp.json() == {} or isinstance(resp.json(), dict)
+
+    async def test_get_setting_by_key(
+        self,
+        client: AsyncClient,
+        admin_user: User,
+        db_session: AsyncSession,
+    ):
+        """Settings dict contains specific key after creation."""
+        setting = SystemSetting(
+            setting_key="csv_delimiter",
+            setting_value=";",
+            setting_type="string",
+        )
+        db_session.add(setting)
+        await db_session.flush()
+
+        resp = await client.get(
+            "/api/settings/", headers=auth_headers(admin_user)
+        )
+        assert resp.status_code == 200
+        assert resp.json()["csv_delimiter"] == ";"
+
+
+class TestUpdateSettings:
+    """PUT /api/settings/ tests."""
+
+    async def test_update_settings(
+        self, client: AsyncClient, admin_user: User
+    ):
+        """Admin can update/create settings."""
+        resp = await client.put(
+            "/api/settings/",
+            headers=auth_headers(admin_user),
+            json={
+                "company_name": "Tielogic Srl",
+                "csv_delimiter": ",",
+            },
+        )
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["message"].startswith("Updated")
+        assert "company_name" in data["updated_keys"]
+        assert "csv_delimiter" in data["updated_keys"]
+
+        # Verify persistence
+        get_resp = await client.get(
+            "/api/settings/", headers=auth_headers(admin_user)
+        )
+        settings = get_resp.json()
+        assert settings["company_name"] == "Tielogic Srl"
+
+    async def test_settings_require_admin(
+        self, client: AsyncClient, maker_user: User
+    ):
+        """Non-admin user cannot update settings."""
+        resp = await client.put(
+            "/api/settings/",
+            headers=auth_headers(maker_user),
+            json={"some_key": "some_value"},
+        )
+        assert resp.status_code == 403