fix(analytics): remove duplicate sessionId index in PageViewSchema

- PageViewSchema had 'index: true' on sessionId field (line 16)
- AND compound index PageViewSchema.index({ sessionId: 1, timestamp: -1 })
- Compound index already covers sessionId queries (leftmost prefix)
- Removed redundant single-field index to eliminate Mongoose warning

src/models/Analytics.model.js

@@ -13,7 +13,7 @@ const PageViewSchema = new mongoose.Schema({
 
   // Visitor Information (privacy-respecting)
   visitorId: { type: String, required: true, index: true }, // Hashed IP + User Agent
-  sessionId: { type: String, required: true, index: true }, // Session identifier
+  sessionId: { type: String, required: true }, // Session identifier (indexed via compound index below)
 
   // Request Details
   userAgent: { type: String },