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/server.js

@@ -1,6 +1,7 @@
 require("dotenv").config();
 const express = require("express");
 const mongoose = require("mongoose");
+const couchdbService = require("./services/couchdbService");
 const cors = require("cors");
 const http = require("http");
 const socketio = require("socket.io");
@@ -58,7 +59,8 @@ const apiLimiter = rateLimit({
   legacyHeaders: false,
 });
 
-// MongoDB Connection
+// Database Connections
+// MongoDB (for backward compatibility during migration)
 mongoose
   .connect(process.env.MONGO_URI, {
     useNewUrlParser: true,
@@ -67,6 +69,11 @@ mongoose
   .then(() => console.log("MongoDB connected"))
   .catch((err) => console.log("MongoDB connection error:", err));
 
+// CouchDB (primary database)
+couchdbService.initialize()
+  .then(() => console.log("CouchDB initialized"))
+  .catch((err) => console.log("CouchDB initialization error:", err));
+
 // Socket.IO Authentication Middleware
 io.use(socketAuth);