fix: suppress OneDrive 404 errors during delta scans as non-provisioned

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>

CHANGELOG.md

@@ -24,6 +24,8 @@ Version numbers follow [Semantic Versioning](https://semver.org/spec/v2.0.0.html
 
 ### Fixed
 
+- **OneDrive 404 errors during delta scans** — `GET /users/{id}/drive/root/delta` returns 404 for users with no OneDrive licence, a disabled service plan, a drive that was never provisioned (account never signed in), or a suspended account. Previously these 404s fell through to `requests.raise_for_status()` and were caught by the generic `except Exception` handler in `_scan_user_onedrive`, broadcasting a red `scan_error` card. Full scans never showed the error because `_iter_drive_folder_for` has a bare `except Exception: return`. Fixed by adding `M365DriveNotFound(M365Error)` to `m365_connector.py`, raising it from `_get()` on HTTP 404, and handling it explicitly in `_scan_user_onedrive` with a `scan_phase` broadcast ("OneDrive (user): not provisioned — skipped") before the generic exception handler.
+
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