feat: two-role system — super_admin & admin program (Fasa 12)

- Replace is_admin boolean with role enum('super_admin','admin') via migration
- ProgramPolicy: admin program can only view/edit/delete own programs
- EnsureIsAdmin: accepts both roles; EnsureSuperAdmin: super_admin only
- UserController + views: super_admin can manage admin accounts
- Sidebar: user management link & role badge gated on isSuperAdmin()
- Fix Controller base class: add AuthorizesRequests trait
- Fix tests: replace nonAdmin() (invalid enum) with adminProgram() against super_admin-only route

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Http/Middleware/EnsureSuperAdmin.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace App\Http\Middleware;
+
+use Closure;
+use Illuminate\Http\Request;
+use Symfony\Component\HttpFoundation\Response;
+
+class EnsureSuperAdmin
+{
+    public function handle(Request $request, Closure $next): Response
+    {
+        if ($request->user()?->role !== 'super_admin') {
+            abort(403, 'Hanya Super Admin boleh mengakses bahagian ini.');
+        }
+
+        return $next($request);
+    }
+}