fix(backend): sync push error handling + validation

- apply_push now uses PRAGMA table_info() to get valid column names per
  table and filters incoming data to only known columns, preventing
  "no such column" SQLite errors from frontend-only fields like oracle_id
- Wrap each operation in try/except so one bad op doesn't abort the
  whole batch; errors are returned in the conflicts list instead of 500
- Add server_default to all NOT NULL float/int columns so raw SQL
  INSERT OR REPLACE without those fields still succeeds
- Align DB models with frontend schema.js:
  - orders: add nr_comanda, client_nume, client_telefon, nr_auto,
    marca_denumire, model_denumire, created_by
  - order_lines: add norma_id, mecanic_id, ordine
  - vehicles: add serie_sasiu, client_cod_fiscal (keep vin, client_cui
    for REST API compat)
  - catalog_*: rename nume → denumire to match frontend schema
  - catalog_norme: align fields (cod, denumire, ore_normate)
  - invoices: add serie_factura, modalitate_plata, client_cod_fiscal,
    nr_auto, total_fara_tva, tva, total_general; keep total for compat
  - appointments: add client_nume, client_telefon, data_ora, durata_minute,
    status, order_id
  - mecanici: add user_id, prenume, activ
- Fix seed.py to use denumire= instead of nome= after catalog rename
- Add 3 new sync push tests covering order insert with frontend fields,
  unknown column filtering, and order_line with norma_id/mecanic_id/ordine

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

backend/app/db/seed.py

@@ -77,28 +77,28 @@ async def seed_catalog(db: AsyncSession, tenant_id: str) -> dict:
     # Marci
     for name in MARCI:
         db.add(
-            CatalogMarca(id=uuid7(), tenant_id=tenant_id, nume=name)
+            CatalogMarca(id=uuid7(), tenant_id=tenant_id, denumire=name)
         )
     counts["marci"] = len(MARCI)
 
     # Ansamble
     for name in ANSAMBLE:
         db.add(
-            CatalogAnsamblu(id=uuid7(), tenant_id=tenant_id, nume=name)
+            CatalogAnsamblu(id=uuid7(), tenant_id=tenant_id, denumire=name)
         )
     counts["ansamble"] = len(ANSAMBLE)
 
     # Tipuri deviz
     for name in TIPURI_DEVIZ:
         db.add(
-            CatalogTipDeviz(id=uuid7(), tenant_id=tenant_id, nume=name)
+            CatalogTipDeviz(id=uuid7(), tenant_id=tenant_id, denumire=name)
         )
     counts["tipuri_deviz"] = len(TIPURI_DEVIZ)
 
     # Tipuri motoare
     for name in TIPURI_MOTOARE:
         db.add(
-            CatalogTipMotor(id=uuid7(), tenant_id=tenant_id, nume=name)
+            CatalogTipMotor(id=uuid7(), tenant_id=tenant_id, denumire=name)
         )
     counts["tipuri_motoare"] = len(TIPURI_MOTOARE)