phsl / new-api

When syncing official models, clicking "Apply overwrite" with zero selected
conflict fields resulted in no request being sent and the modal simply closing.
This blocked creation of missing models/vendors even though the backend
supports an empty `overwrite` array and will still create missing items.

Changes:
- Remove the early-return guard in `UpstreamConflictModal.handleOk`
- Always call `onSubmit(payload)` even when `payload` is empty
- Keep closing behavior when the request succeeds

Behavior:
- Users can now proceed with upstream sync without selecting any conflict fields
- Missing models/vendors are created as expected
- Existing models are not overwritten unless fields are explicitly selected

Affected:
- web/src/components/table/models/modals/UpstreamConflictModal.jsx

Quality:
- Lint passes
- No breaking changes
- No visual/UI changes beyond the intended behavior

Test plan:
1) Open official models sync and trigger a conflicts preview
2) Click "Apply overwrite" without selecting any fields
3) Expect the sync to proceed and a success toast indicating created models
4) Re-try with some fields selected to confirm overwrites still work