feat: DSC enrollment + MFA controls, user CRUD UX, auth error hardening

- DSC module: list/enroll/revoke dialogs and dsc.service (m_bank_user_dsc API)
- Access control: DSC + MFA toggles via disable-confirm-dialog
- Two-factor auth: expanded UX (DSC + OTP flows)
- Users: create/edit form polish, success snackbar on edit, DSC widget
  retained only inside dsc/ (removed from view-user)
- Auth: X-Requested-With added globally; error handler null-safe on
  empty 500 bodies

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

src/main.scss

@@ -1067,3 +1067,18 @@ mat-card {
   background: rgb(2 6 23 / 75%) !important;
   backdrop-filter: blur(4px);
 }
+
+/* ─── DSC Enroll Dialog Panel — edge-to-edge hero ─── */
+.ed-dialog-panel {
+  .mat-mdc-dialog-container {
+    padding: 0;
+    border-radius: 16px;
+    overflow: hidden;
+  }
+
+  .mat-mdc-dialog-surface {
+    padding: 0 !important;
+    border-radius: 16px !important;
+    overflow: hidden !important;
+  }
+}