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/js/locales/en.json

@@ -0,0 +1,76 @@
+{
+  "numpad": {
+    "title": "Numeric Keypad",
+    "clear": "Clear",
+    "submit": "Confirm",
+    "decimal": "Decimal",
+    "close": "Close"
+  },
+  "measurement": {
+    "pass": "Pass",
+    "warning": "Warning",
+    "fail": "Fail",
+    "value": "Value",
+    "next": "Next measurement"
+  },
+  "common": {
+    "loading": "Loading...",
+    "save": "Save",
+    "cancel": "Cancel",
+    "confirm": "Confirm",
+    "delete": "Delete",
+    "edit": "Edit",
+    "search": "Search...",
+    "noResults": "No results",
+    "close": "Close",
+    "error": "Error",
+    "success": "Success",
+    "warning": "Warning",
+    "info": "Info",
+    "page": "Page",
+    "of": "of",
+    "previous": "Previous",
+    "next": "Next"
+  },
+  "theme": {
+    "light": "Light",
+    "dark": "Dark",
+    "toggle": "Toggle theme"
+  },
+  "language": {
+    "switch": "Switch language",
+    "it": "Italian",
+    "en": "English"
+  },
+  "auth": {
+    "login": "Sign in to your account",
+    "username": "Username",
+    "password": "Password",
+    "signIn": "Sign In",
+    "invalidCredentials": "Invalid credentials",
+    "enterCredentials": "Enter username and password",
+    "forgotPassword": "Forgot password? Contact administrator",
+    "welcome": "Welcome, {name}!",
+    "logoutSuccess": "Logged out successfully",
+    "loginRequired": "Please log in to continue"
+  },
+  "nav": {
+    "measurements": "Measurements",
+    "recipes": "Recipes",
+    "statistics": "Statistics",
+    "admin": "Admin",
+    "users": "Users",
+    "settings": "Settings",
+    "profile": "Profile",
+    "logout": "Logout"
+  },
+  "profile": {
+    "title": "User Profile",
+    "displayName": "Display Name",
+    "language": "Language",
+    "theme": "Theme",
+    "roles": "Roles",
+    "saveChanges": "Save Changes",
+    "updateSuccess": "Profile updated successfully"
+  }
+}

src/frontend/flask_app/static/js/locales/it.json

@@ -0,0 +1,76 @@
+{
+  "numpad": {
+    "title": "Tastierino Numerico",
+    "clear": "Cancella",
+    "submit": "Conferma",
+    "decimal": "Virgola",
+    "close": "Chiudi"
+  },
+  "measurement": {
+    "pass": "Conforme",
+    "warning": "Attenzione",
+    "fail": "Non Conforme",
+    "value": "Valore",
+    "next": "Prossima misura"
+  },
+  "common": {
+    "loading": "Caricamento...",
+    "save": "Salva",
+    "cancel": "Annulla",
+    "confirm": "Conferma",
+    "delete": "Elimina",
+    "edit": "Modifica",
+    "search": "Cerca...",
+    "noResults": "Nessun risultato",
+    "close": "Chiudi",
+    "error": "Errore",
+    "success": "Successo",
+    "warning": "Attenzione",
+    "info": "Info",
+    "page": "Pagina",
+    "of": "di",
+    "previous": "Precedente",
+    "next": "Successivo"
+  },
+  "theme": {
+    "light": "Chiaro",
+    "dark": "Scuro",
+    "toggle": "Cambia tema"
+  },
+  "language": {
+    "switch": "Cambia lingua",
+    "it": "Italiano",
+    "en": "English"
+  },
+  "auth": {
+    "login": "Accedi al sistema",
+    "username": "Username",
+    "password": "Password",
+    "signIn": "Accedi",
+    "invalidCredentials": "Credenziali non valide",
+    "enterCredentials": "Inserisci username e password",
+    "forgotPassword": "Hai dimenticato la password? Contatta l'amministratore",
+    "welcome": "Benvenuto, {name}!",
+    "logoutSuccess": "Logout effettuato",
+    "loginRequired": "Effettua il login per continuare"
+  },
+  "nav": {
+    "measurements": "Misure",
+    "recipes": "Ricette",
+    "statistics": "Statistiche",
+    "admin": "Admin",
+    "users": "Utenti",
+    "settings": "Impostazioni",
+    "profile": "Profilo",
+    "logout": "Esci"
+  },
+  "profile": {
+    "title": "Profilo Utente",
+    "displayName": "Nome Visualizzato",
+    "language": "Lingua",
+    "theme": "Tema",
+    "roles": "Ruoli",
+    "saveChanges": "Salva Modifiche",
+    "updateSuccess": "Profilo aggiornato con successo"
+  }
+}