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/barcode.js

@@ -0,0 +1,134 @@
+/**
+ * Barcode Scanner Manager
+ * Integration with html5-qrcode library
+ * Supports QR codes, barcodes, and camera scanning
+ */
+
+function barcodeScanner() {
+  const _t = (key) => (window.BARCODE_I18N && window.BARCODE_I18N[key]) || key;
+
+  return {
+    scanning: false,
+    result: null,
+    error: null,
+    scanner: null,
+    cameraId: null,
+
+    async startScan() {
+      this.scanning = true;
+      this.result = null;
+      this.error = null;
+
+      // Check library availability
+      if (!window.Html5Qrcode) {
+        this.error = _t('scanner_lib_not_loaded');
+        this.scanning = false;
+        return;
+      }
+
+      try {
+        // Get available cameras
+        const devices = await Html5Qrcode.getCameras();
+
+        if (!devices || devices.length === 0) {
+          this.error = _t('no_camera_available');
+          this.scanning = false;
+          return;
+        }
+
+        // Prefer back camera
+        const backCamera = devices.find(d => d.label.toLowerCase().includes('back'));
+        this.cameraId = backCamera ? backCamera.id : devices[0].id;
+
+        // Initialize scanner
+        this.scanner = new Html5Qrcode("barcode-reader");
+
+        // Start scanning
+        await this.scanner.start(
+          this.cameraId,
+          {
+            fps: 10,
+            qrbox: { width: 250, height: 250 },
+            aspectRatio: 1.0
+          },
+          (decodedText, decodedResult) => {
+            // Success callback
+            this.result = decodedText;
+            this.stopScan();
+
+            // Dispatch event for parent components
+            this.$dispatch('barcode-scanned', {
+              code: decodedText,
+              format: decodedResult.result?.format?.formatName || 'unknown',
+              timestamp: new Date().toISOString()
+            });
+          },
+          (errorMessage) => {
+            // Error callback - ignore continuous scanning errors
+            // Only log non-routine errors
+            if (!errorMessage.includes('NotFoundException')) {
+              console.debug('Scan frame error:', errorMessage);
+            }
+          }
+        );
+
+      } catch (err) {
+        console.error('Scanner initialization error:', err);
+        this.error = _t('camera_access_error');
+        this.scanning = false;
+      }
+    },
+
+    async stopScan() {
+      if (this.scanner) {
+        try {
+          await this.scanner.stop();
+          await this.scanner.clear();
+        } catch (err) {
+          console.error('Stop scan error:', err);
+        }
+        this.scanner = null;
+      }
+      this.scanning = false;
+    },
+
+    clear() {
+      this.result = null;
+      this.error = null;
+    },
+
+    // Cleanup on component destroy
+    destroy() {
+      this.stopScan();
+    }
+  };
+}
+
+/**
+ * Barcode Input Helper
+ * For integrating barcode scanning into input fields
+ */
+function barcodeInput() {
+  return {
+    value: '',
+    showScanner: false,
+
+    openScanner() {
+      this.showScanner = true;
+    },
+
+    handleScan(event) {
+      this.value = event.detail.code;
+      this.showScanner = false;
+
+      // Dispatch value change event
+      this.$dispatch('input', { value: this.value });
+      this.$dispatch('change', { value: this.value });
+    },
+
+    clear() {
+      this.value = '';
+      this.$dispatch('input', { value: '' });
+    }
+  };
+}