feat: migrate Event and Reward models from MongoDB to CouchDB

- Replace Event model with CouchDB version using couchdbService
- Replace Reward model with CouchDB version using couchdbService
- Update event and reward routes to use new model interfaces
- Handle participant management with embedded user data
- Maintain status transitions for events (upcoming, ongoing, completed, cancelled)
- Preserve catalog functionality and premium vs regular rewards
- Update validators to accept CouchDB document IDs
- Add rewards design document to couchdbService
- Update test helpers for new model structure
- Initialize CouchDB alongside MongoDB in server.js for backward compatibility
- Fix linting issues in migrated routes

🤖 Generated with [AI Assistant]

Co-Authored-By: AI Assistant <noreply@ai-assistant.com>

backend/services/couchdbService.js

@@ -321,6 +321,37 @@ class CouchDBService {
           }
         }
       },
+      {
+        _id: "_design/rewards",
+        views: {
+          "by-cost": {
+            map: `function(doc) {
+              if (doc.type === "reward" && doc.cost) {
+                emit(doc.cost, doc);
+              }
+            }`
+          },
+          "by-premium": {
+            map: `function(doc) {
+              if (doc.type === "reward" && doc.isPremium) {
+                emit(doc.isPremium, doc);
+              }
+            }`
+          }
+        },
+        indexes: {
+          "rewards-by-cost": {
+            index: { fields: ["type", "cost"] },
+            name: "rewards-by-cost",
+            type: "json"
+          },
+          "rewards-by-premium": {
+            index: { fields: ["type", "isPremium"] },
+            name: "rewards-by-premium",
+            type: "json"
+          }
+        }
+      },
       {
         _id: "_design/general",
         indexes: {