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/FileTransfer.razor

@@ -3,6 +3,7 @@
 @inject IUserSessionService Session
 @inject IUserContextAccessor UserContext
 @inject ISessionManager SessionMgr
+@inject IElevationCoordinator Elevation
 @inject IFileTransferService TransferSvc
 @rendermode InteractiveServer
 
@@ -119,8 +120,6 @@
         {
             var srcUrl = string.IsNullOrWhiteSpace(_srcSiteUrl) ? Session.CurrentProfile!.TenantUrl : _srcSiteUrl.Trim();
             var dstUrl = string.IsNullOrWhiteSpace(_dstSiteUrl) ? Session.CurrentProfile!.TenantUrl : _dstSiteUrl.Trim();
-            var srcCtx = await SessionMgr.GetOrCreateContextAsync(srcUrl, Session.CurrentProfile!, _cts.Token);
-            var dstCtx = await SessionMgr.GetOrCreateContextAsync(dstUrl, Session.CurrentProfile!, _cts.Token);
             var job = new TransferJob
             {
                 SourceSiteUrl = srcUrl, SourceLibrary = _srcLibrary, SourceFolderPath = _srcFolder,
@@ -129,7 +128,13 @@
                 ConflictPolicy = _conflict == "Overwrite" ? ConflictPolicy.Overwrite : _conflict == "Rename" ? ConflictPolicy.Rename : ConflictPolicy.Skip,
                 IncludeSourceFolder = _includeSourceFolder
             };
-            _summary = await TransferSvc.TransferAsync(srcCtx, dstCtx, job, progress, _cts.Token);
+            _summary = await Elevation.RunAsync(async c =>
+            {
+                // Closure rebuilds both contexts each attempt so an elevated retry re-issues cleanly.
+                var srcCtx = await SessionMgr.GetOrCreateContextAsync(srcUrl, Session.CurrentProfile!, c);
+                var dstCtx = await SessionMgr.GetOrCreateContextAsync(dstUrl, Session.CurrentProfile!, c);
+                return await TransferSvc.TransferAsync(srcCtx, dstCtx, job, progress, c);
+            }, _cts.Token);
             _status = $"Complete: {_summary.SuccessCount} transferred.";
         }
         catch (OperationCanceledException) { _status = "Cancelled."; }