feat(backend): PDF deviz + portal client + SMS + invoice service

- PDF generation with WeasyPrint: deviz and factura templates (A4, branding)
- GET /orders/{id}/pdf/deviz returns PDF with order lines and totals
- Client portal (public, no auth): GET /p/{token}, POST /p/{token}/accept|reject
- SMS service (SMSAPI.ro) - skips in dev when no token configured
- Invoice service: create from validated order, auto-number (F-YYYY-NNNN)
- GET /invoices/{id}/pdf returns factura PDF
- Order status_client field for client accept/reject tracking
- Alembic migration for status_client
- 19 passing tests (auth + sync + orders + pdf + portal + invoices)

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

backend/app/db/models/order.py

@@ -17,3 +17,4 @@ class Order(Base, UUIDMixin, TenantMixin, TimestampMixin):
     total_materiale: Mapped[float] = mapped_column(Float, default=0)
     total_general: Mapped[float] = mapped_column(Float, default=0)
     token_client: Mapped[str | None] = mapped_column(String(36))
+    status_client: Mapped[str | None] = mapped_column(String(20))