fix: remove Sidebar unread count setInterval HTTP polling

[Pratyush-Panda-2006]

Fixes #874

Description

This PR removes the periodic setInterval blocks that fire HTTP requests every 10 seconds in Sidebar.tsx to fetch unread badge counts.

Instead of polling the database continuously, count synchronization is now fully event-driven, leveraging:

1. Real-time WebSockets: Listening to notification:new, conversation_read, conversation:deleted, and conversation:participant_deleted to dynamically update counts.
2. Custom Browser Events: Using lightweight "notifications:read" and "messages:read" custom events to sync counts immediately when the user reads notifications or messages locally.
3. Navigation/Pathname Updates: Fetching the latest counts when route transitions occur.

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[Shivayan09]

Code fails CI pipeline workflow