Add M365DriveNotFound(M365Error) exception raised by _get() on HTTP 404.
Catch it explicitly in _scan_user_onedrive before the generic handler,
broadcasting a scan_phase ("not provisioned — skipped") instead of a red
scan_error card. Full-scan path is unaffected (bare except Exception: return
in _iter_drive_folder_for already silenced the same 404).
Root cause: _get() fell through to raise_for_status() on 404, caught by
the generic except Exception handler and broadcast as scan_error. The
asymmetry with full scans (which silently skipped 404s) was confusing.
Common causes of OneDrive 404: no licence assigned, service plan disabled,
drive never provisioned (account never signed in), account suspended.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
