Adds a `GrantSource Source { get; set; }` property (defaults to
`GrantSource.Unknown`) to `InventoryLoadConfig`. Plumbing-only — no
behavior change; callers that don't set `Source` get Unknown rows,
greppable via `acquire_type=0` in dev.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>