feat: add admin user system with role-based access control

Implement comprehensive admin user system for Kubernetes deployment:

Backend:
- Add isAdmin field to User model for role-based permissions
- Create adminAuth middleware to protect admin-only routes
- Protect 11 routes across rewards, cache, streets, and analytics endpoints
- Update setup-couchdb.js to seed default admin user at deployment

Kubernetes:
- Add ADMIN_EMAIL and ADMIN_PASSWORD to secrets.yaml
- Add ADMIN_EMAIL to configmap.yaml for non-sensitive config
- Create couchdb-init-job.yaml for automated database initialization
- Update secrets.yaml.example with admin user documentation

Frontend:
- Create AdminRoute component for admin-only page protection
- Create comprehensive AdminDashboard with 5 tabs:
  * Overview: Platform statistics and quick actions
  * Users: List, search, manage admin status, delete users
  * Streets: Create, edit, delete streets
  * Rewards: Create, edit, toggle, delete rewards
  * Content: Moderate posts and events
- Add Admin navigation link in Navbar (visible only to admins)
- Integrate admin routes in App.js

Default admin user:
- Email: will@wills-portal.com
- Created automatically by K8s init job at deployment

Routes protected:
- POST/PUT/DELETE /api/rewards (catalog management)
- POST /api/streets (street creation)
- DELETE /api/cache (cache operations)
- GET /api/analytics/* (platform statistics)

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

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

backend/models/User.js

@@ -47,8 +47,9 @@ class User {
 
 
     // --- Gamification & App Data ---
-    this.isPremium = data.isPremium || false;
-    this.points = Math.max(0, data.points || 0);
+     this.isPremium = data.isPremium || false;
+     this.isAdmin = data.isAdmin || false;
+     this.points = Math.max(0, data.points || 0);
     this.adoptedStreets = data.adoptedStreets || [];
     this.completedTasks = data.completedTasks || [];
     this.posts = data.posts || [];
@@ -205,10 +206,11 @@ class User {
       location: this.location,
       website: this.website,
       social: this.social,
-      privacySettings: this.privacySettings,
-      preferences: this.preferences,
-      isPremium: this.isPremium,
-      points: this.points,
+       privacySettings: this.privacySettings,
+       preferences: this.preferences,
+       isPremium: this.isPremium,
+       isAdmin: this.isAdmin,
+       points: this.points,
       adoptedStreets: this.adoptedStreets,
       completedTasks: this.completedTasks,
       posts: this.posts,