feat: add clients nomenclator, order edit/delete/devalidate, invoice types, dashboard redesign

- New clients table with PF/PJ support, fiscal data (CUI, IBAN, eFactura fields)
- Full CRUD API for clients with search, sync integration
- Order lifecycle: edit header (DRAFT), devalidate (VALIDAT→DRAFT), delete order/invoice
- Invoice types: FACTURA (B2B) vs BON_FISCAL (B2C) with different nr formats
- OrderCreateView redesigned as multi-step flow (client→vehicle→details)
- Autocomplete from catalog_norme/catalog_preturi in OrderLineForm
- Dashboard now combines stats + full orders table with filter tabs and search
- ClientPicker and VehiclePicker with inline creation capability
- Frontend schema aligned with backend (missing columns causing sync errors)
- Mobile responsive fixes for OrderDetailView buttons

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/db/models/__init__.py

@@ -1,5 +1,6 @@
 from app.db.models.tenant import Tenant
 from app.db.models.user import User
+from app.db.models.client import Client
 from app.db.models.vehicle import Vehicle
 from app.db.models.order import Order
 from app.db.models.order_line import OrderLine
@@ -20,6 +21,7 @@ from app.db.models.invite import InviteToken
 __all__ = [
     "Tenant",
     "User",
+    "Client",
     "Vehicle",
     "Order",
     "OrderLine",