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>

m365_connector.py

@@ -93,6 +93,17 @@ class M365DeltaTokenExpired(M365Error):
     pass
 
 
+class M365DriveNotFound(M365Error):
+    """Raised when the Graph API returns 404 for a drive/root path.
+
+    Common causes: OneDrive licence not assigned, service plan disabled,
+    drive not yet provisioned (user has never signed in), or account
+    suspended/deleted.  Not a scan error — callers should skip the user
+    and log at a lower severity.
+    """
+    pass
+
+
 class M365Connector:
     def __init__(self, client_id: str, tenant_id: str, client_secret: str = ""):
         if not MSAL_OK:
@@ -425,6 +436,8 @@ class M365Connector:
                 except Exception:
                     msg = r.text[:200]
                 raise M365PermissionError(path, msg)
+            if r.status_code == 404:
+                raise M365DriveNotFound(f"404 Not Found: {path}")
             r.raise_for_status()
             return r.json()
         raise _requests.exceptions.RetryError(f"Gave up after {self._MAX_RETRIES} attempts: {url}")