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/__tests__/utils/testHelpers.js

@@ -134,12 +134,20 @@ async function createTestEvent(userId, overrides = {}) {
   const defaultEvent = {
     title: 'Test Event',
     description: 'Test event description',
-    date: new Date(Date.now() + 86400000), // Tomorrow
+    date: new Date(Date.now() + 86400000).toISOString(), // Tomorrow
     location: 'Test Location',
-    organizer: userId,
   };
 
   const event = await Event.create({ ...defaultEvent, ...overrides });
+  
+  // Add participant if userId is provided
+  if (userId) {
+    const user = await User.findById(userId);
+    if (user) {
+      await Event.addParticipant(event._id, userId, user.name, user.profilePicture || '');
+    }
+  }
+  
   return event;
 }
 
@@ -150,10 +158,17 @@ async function createTestReward(overrides = {}) {
   const defaultReward = {
     name: 'Test Reward',
     description: 'Test reward description',
-    pointsCost: 100,
+    cost: 100,
   };
 
-  const reward = await Reward.create({ ...defaultReward, ...overrides });
+  // Handle legacy field name mapping
+  const rewardData = { ...defaultReward, ...overrides };
+  if (rewardData.pointsCost && !rewardData.cost) {
+    rewardData.cost = rewardData.pointsCost;
+    delete rewardData.pointsCost;
+  }
+
+  const reward = await Reward.create(rewardData);
   return reward;
 }