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/static/img/tmflow-icon.svg

@@ -0,0 +1,27 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32" fill="none">
+  <!-- Stylized Caliper Icon for Favicon -->
+
+  <!-- Caliper outer frame -->
+  <rect x="2" y="3" width="5" height="26" rx="1.5" fill="#2563EB"/>
+  <rect x="2" y="3" width="19" height="5" rx="1.5" fill="#2563EB"/>
+  <rect x="2" y="24" width="19" height="5" rx="1.5" fill="#2563EB"/>
+
+  <!-- Sliding jaw -->
+  <rect x="12" y="8" width="4.5" height="6.5" rx="1" fill="#1E40AF"/>
+  <rect x="12" y="17.5" width="4.5" height="6.5" rx="1" fill="#1E40AF"/>
+
+  <!-- Depth rod -->
+  <rect x="4" y="14" width="12" height="3.5" rx="1" fill="#3B82F6" opacity="0.55"/>
+
+  <!-- Scale markings -->
+  <rect x="8" y="5" width="1" height="2.5" rx="0.5" fill="#FFFFFF" opacity="0.65"/>
+  <rect x="11" y="5" width="1" height="2.5" rx="0.5" fill="#FFFFFF" opacity="0.65"/>
+  <rect x="14" y="5" width="1" height="2.5" rx="0.5" fill="#FFFFFF" opacity="0.65"/>
+  <rect x="17" y="5" width="1" height="2.5" rx="0.5" fill="#FFFFFF" opacity="0.65"/>
+
+  <!-- Flow arrow -->
+  <path d="M22 16 C25 16, 26.5 11, 29 11"
+        stroke="#3B82F6" stroke-width="2.2" stroke-linecap="round" fill="none"/>
+  <path d="M27 8.5 L29.5 11 L27 13.5"
+        stroke="#3B82F6" stroke-width="1.8" stroke-linecap="round" stroke-linejoin="round" fill="none"/>
+</svg>