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/sync/router.py

@@ -0,0 +1,41 @@
+from datetime import UTC, datetime
+
+from fastapi import APIRouter, Depends, Query
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.db.session import get_db
+from app.deps import get_tenant_id
+from app.sync import schemas, service
+
+router = APIRouter()
+
+
+@router.get("/full")
+async def sync_full(
+    tenant_id: str = Depends(get_tenant_id),
+    db: AsyncSession = Depends(get_db),
+):
+    tables = await service.get_full(db, tenant_id)
+    return {"tables": tables, "synced_at": datetime.now(UTC).isoformat()}
+
+
+@router.get("/changes")
+async def sync_changes(
+    since: str = Query(...),
+    tenant_id: str = Depends(get_tenant_id),
+    db: AsyncSession = Depends(get_db),
+):
+    tables = await service.get_changes(db, tenant_id, since)
+    return {"tables": tables, "synced_at": datetime.now(UTC).isoformat()}
+
+
+@router.post("/push", response_model=schemas.SyncPushResponse)
+async def sync_push(
+    data: schemas.SyncPushRequest,
+    tenant_id: str = Depends(get_tenant_id),
+    db: AsyncSession = Depends(get_db),
+):
+    result = await service.apply_push(
+        db, tenant_id, [op.model_dump() for op in data.operations]
+    )
+    return result