Wire auto-elevate ownership across all SharePoint operations

The "Auto-elevate ownership when permission scan is denied" setting was
dead code: the toggle was persisted but never read, the audit flow never
passed its onAccessDenied callback, and EnrichException wrapped every CSOM
error (including ServerUnauthorizedAccessException) into a generic
InvalidOperationException so the access-denied catch could never match.

Centralize elevation instead of per-call-site callbacks:

- Throw typed SharePointAccessDeniedException from EnrichException on
  access-denied, preserving the failing site URL and enriched diagnostic.
- Add scoped IElevationCoordinator that catches it, and when AutoTakeOwnership
  is enabled takes site-collection admin via the tenant admin endpoint and
  retries the operation once. Per-site dedupe prevents loops; admin-host
  denials are not treated as ownership issues. Retry is safe because each
  wrapped operation closure re-issues its own CSOM loads.
- Wrap all site-scoped operations (Storage, Permissions, Duplicates, Search,
  VersionCleanup, FolderStructure, BulkMembers, FileTransfer, Templates) and
  the UserAccessAudit per-site scan in the coordinator.
- Drop the unused onAccessDenied parameter from IUserAccessAuditService.

Elevation still requires SharePoint tenant admin rights on the signed-in
account; the coordinator surfaces a clear message when that is missing.

Also keeps the prior StorageService change that avoids admin-gated
folder.StorageMetrics (403 for delegated non-admin tokens).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Components/Pages/BulkMembers.razor

@@ -3,6 +3,7 @@
 @inject IUserSessionService Session
 @inject IUserContextAccessor UserContext
 @inject ISessionManager SessionMgr
+@inject IElevationCoordinator Elevation
 @inject IBulkMemberService BulkSvc
 @inject ICsvValidationService CsvValidation
 @inject BulkResultCsvExportService ExportSvc
@@ -97,8 +98,11 @@
         var progress = new Progress<OperationProgress>(p => { _status = p.Message; _current = p.Current; _total = p.Total; InvokeAsync(StateHasChanged); });
         try
         {
-            var ctx = await SessionMgr.GetOrCreateContextAsync(siteUrl, Session.CurrentProfile!, _cts.Token);
-            _summary = await BulkSvc.AddMembersAsync(ctx, Session.CurrentProfile!, validRows, progress, _cts.Token);
+            _summary = await Elevation.RunAsync(async c =>
+            {
+                var ctx = await SessionMgr.GetOrCreateContextAsync(siteUrl, Session.CurrentProfile!, c);
+                return await BulkSvc.AddMembersAsync(ctx, Session.CurrentProfile!, validRows, progress, c);
+            }, _cts.Token);
             _status = $"Complete: {_summary.SuccessCount} added, {_summary.FailedCount} failed.";
         }
         catch (OperationCanceledException) { _status = "Cancelled."; }