feat(backend): sync endpoints + all models + seed + order workflow

- All business models: Vehicle, Order, OrderLine, Invoice, Appointment,
  CatalogMarca/Model/Ansamblu/Norma/Pret/TipDeviz/TipMotor, Mecanic
- Sync endpoints: GET /sync/full, GET /sync/changes?since=, POST /sync/push
  with tenant isolation and last-write-wins conflict resolution
- Order CRUD with state machine: DRAFT -> VALIDAT -> FACTURAT
  Auto-recalculates totals (manopera + materiale)
- Vehicle CRUD: list, create, get, update
- Seed data: 24 marci, 11 ansamble, 6 tipuri deviz, 5 tipuri motoare, 3 preturi
- Alembic migration for all business models
- 13 passing tests (auth + sync + orders)

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

backend/app/db/models/order.py

@@ -0,0 +1,19 @@
+from sqlalchemy import Float, Integer, String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db.base import Base, UUIDMixin, TenantMixin, TimestampMixin
+
+
+class Order(Base, UUIDMixin, TenantMixin, TimestampMixin):
+    __tablename__ = "orders"
+    vehicle_id: Mapped[str] = mapped_column(String(36))
+    tip_deviz_id: Mapped[str | None] = mapped_column(String(36))
+    status: Mapped[str] = mapped_column(String(20), default="DRAFT")
+    data_comanda: Mapped[str | None] = mapped_column(Text)
+    km_intrare: Mapped[int | None] = mapped_column(Integer)
+    observatii: Mapped[str | None] = mapped_column(Text)
+    mecanic_id: Mapped[str | None] = mapped_column(String(36))
+    total_manopera: Mapped[float] = mapped_column(Float, default=0)
+    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))