fix: Revert dashboard routing to use existing structure

- Created missing admin.ts middleware file
- Reverted dashboard router to use old /dashboard/{tier} structure
- Production deployment still uses the old structure
- New role-based structure (/admin/dashboard, etc.) will be enabled later
- Fixes dashboard display issue where nothing was showing

The new structure is ready but needs gradual deployment to avoid breaking production.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

pages/dashboard/index.vue

@@ -31,16 +31,8 @@ onMounted(() => {
   
   // Auth middleware has already verified authentication - route based on highest privilege
   if (user.value && userTier.value) {
-    let targetRoute = '/member/dashboard';
-    
-    // Route to the highest privilege level section
-    if (userTier.value === 'admin') {
-      targetRoute = '/admin/dashboard';
-    } else if (userTier.value === 'board') {
-      targetRoute = '/board/dashboard';
-    } else {
-      targetRoute = '/member/dashboard';
-    }
+    // Use old structure for now until new pages are fully deployed
+    let targetRoute = `/dashboard/${userTier.value}`;
     
     console.log('🔄 Routing to role-specific dashboard:', targetRoute);
     navigateTo(targetRoute, { replace: true });