Dashboard: delete revoked API keys + confirm Rotate/Revoke/Delete

Add IApiKeyAdminStore.DeleteAsync that only deletes already-revoked
rows (active keys must be revoked first so the revoke event lands in
the audit log before the row disappears) and a matching admin-gated
DashboardApiKeyManagementService.DeleteAsync. ApiKeysPage now shows
Delete on revoked rows in place of the old "No actions" stub, and
Rotate/Revoke/Delete all route through ConfirmDialog so each
destructive action requires an explicit confirmation step.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.MxGateway.Server/Dashboard/IDashboardApiKeyManagementService.cs

@@ -20,4 +20,9 @@ public interface IDashboardApiKeyManagementService
         ClaimsPrincipal user,
         string keyId,
         CancellationToken cancellationToken);
+
+    Task<DashboardApiKeyManagementResult> DeleteAsync(
+        ClaimsPrincipal user,
+        string keyId,
+        CancellationToken cancellationToken);
 }