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/catalog.py

@@ -0,0 +1,44 @@
+from sqlalchemy import Float, String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db.base import Base, UUIDMixin, TenantMixin, TimestampMixin
+
+
+class CatalogMarca(Base, UUIDMixin, TenantMixin, TimestampMixin):
+    __tablename__ = "catalog_marci"
+    nume: Mapped[str] = mapped_column(String(100))
+
+
+class CatalogModel(Base, UUIDMixin, TimestampMixin):
+    __tablename__ = "catalog_modele"
+    marca_id: Mapped[str] = mapped_column(String(36), index=True)
+    nume: Mapped[str] = mapped_column(String(100))
+
+
+class CatalogAnsamblu(Base, UUIDMixin, TenantMixin, TimestampMixin):
+    __tablename__ = "catalog_ansamble"
+    nume: Mapped[str] = mapped_column(String(100))
+
+
+class CatalogNorma(Base, UUIDMixin, TenantMixin, TimestampMixin):
+    __tablename__ = "catalog_norme"
+    ansamblu_id: Mapped[str] = mapped_column(String(36), index=True)
+    descriere: Mapped[str] = mapped_column(Text)
+    ore: Mapped[float] = mapped_column(Float, default=0)
+
+
+class CatalogPret(Base, UUIDMixin, TenantMixin, TimestampMixin):
+    __tablename__ = "catalog_preturi"
+    denumire: Mapped[str] = mapped_column(String(200))
+    pret: Mapped[float] = mapped_column(Float, default=0)
+    um: Mapped[str] = mapped_column(String(10))
+
+
+class CatalogTipDeviz(Base, UUIDMixin, TenantMixin, TimestampMixin):
+    __tablename__ = "catalog_tipuri_deviz"
+    nume: Mapped[str] = mapped_column(String(100))
+
+
+class CatalogTipMotor(Base, UUIDMixin, TenantMixin, TimestampMixin):
+    __tablename__ = "catalog_tipuri_motoare"
+    nume: Mapped[str] = mapped_column(String(50))