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/routes/streets.js

@@ -3,6 +3,7 @@ const Street = require("../models/Street");
 const User = require("../models/User");
 const couchdbService = require("../services/couchdbService");
 const auth = require("../middleware/auth");
+const adminAuth = require("../middleware/adminAuth");
 const { asyncHandler } = require("../middleware/errorHandler");
 const {
   createStreetValidation,
@@ -103,6 +104,7 @@ router.get(
 router.post(
   "/",
   auth,
+  adminAuth,
   createStreetValidation,
   asyncHandler(async (req, res) => {
     const { name, location } = req.body;