refactor: marketplace release polish

Sprint 28, scoped to admin/* (user decision — full marketplace audit
declined in favor of a bounded pass over the 8 admin features from
Sprints 20-27).

- a11y: aria-label added to every bare <select> not already inside a
  <label> across categories/products/orders/transactions/users/monitoring
- loading states: app-skeleton rows/cards added to list pages that
  previously rendered blank during the initial fetch (categories, orders,
  transactions, users, monitoring's event feed, analytics summary cards)
- admin-dashboard-card's custom shimmer CSS replaced with the shared
  SkeletonComponent (same visual result, one less duplicated animation)
- bundle-size budget warning (~198kB over) confirmed pre-existing —
  present at Sprint 20's first build before any admin/* code existed,
  and new admin pages are all lazy-loaded — documented as out of scope
  for this pass rather than chased

docs/ADMIN.md + docs/SPRINT-PLAN.md updated with the scope decision and
what was explicitly not done (Lighthouse, animations, SEO/sitemap,
storefront/editor a11y).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/features/admin/users/pages/admin-users-page.component.html

@@ -1,6 +1,13 @@
 <section class="admin-users-page">
   <div class="card">
     <h2>{{ 'adminUsers.title' | translate }}</h2>
+    @if (facade.loading()) {
+      <div class="skeleton-rows">
+        @for (i of [1,2,3]; track i) { <app-skeleton shape="rect" height="40px" /> }
+      </div>
+    } @else if (facade.users().length === 0) {
+      <app-empty-state [title]="'adminUsers.emptyTitle' | translate" [description]="'adminUsers.emptyDescription' | translate" />
+    } @else {
     <app-table>
       <thead>
         <tr>
@@ -18,7 +25,7 @@
             <td>{{ user.name }}<br /><small>{{ user.telegramUsername }}</small></td>
             <td>{{ ('adminUsers.scopeValue.' + user.scope) | translate }}</td>
             <td>
-              <select [ngModel]="user.roleId" (ngModelChange)="facade.setRole(user.id, $event)">
+              <select [attr.aria-label]="'adminUsers.role' | translate" [ngModel]="user.roleId" (ngModelChange)="facade.setRole(user.id, $event)">
                 @for (role of facade.roles(); track role.id) {
                   <option [value]="role.id">{{ role.name }}</option>
                 }
@@ -35,6 +42,7 @@
         }
       </tbody>
     </app-table>
+    }
   </div>
 
   <div class="card">
@@ -42,12 +50,12 @@
     <p class="hint">{{ 'adminUsers.passwordlessHint' | translate }}</p>
     <div class="invite-form">
       <app-input type="email" [ngModel]="inviteEmail()" (ngModelChange)="inviteEmail.set($event)" [placeholder]="'adminUsers.email' | translate" />
-      <select [ngModel]="inviteRoleId()" (ngModelChange)="inviteRoleId.set($event)">
+      <select [attr.aria-label]="'adminUsers.role' | translate" [ngModel]="inviteRoleId()" (ngModelChange)="inviteRoleId.set($event)">
         @for (role of facade.roles(); track role.id) {
           <option [value]="role.id">{{ role.name }}</option>
         }
       </select>
-      <select [ngModel]="inviteScope()" (ngModelChange)="inviteScope.set($event)">
+      <select [attr.aria-label]="'adminUsers.scope' | translate" [ngModel]="inviteScope()" (ngModelChange)="inviteScope.set($event)">
         <option value="marketplace">{{ 'adminUsers.scopeValue.marketplace' | translate }}</option>
         <option value="office">{{ 'adminUsers.scopeValue.office' | translate }}</option>
       </select>
@@ -79,6 +87,8 @@
           }
         </tbody>
       </app-table>
+    } @else {
+      <app-empty-state [title]="'adminUsers.invitationsEmptyTitle' | translate" />
     }
   </div>