feat: implement realtime notification and activity infrastructure

[saidai-bhuvanesh]

Overview

This PR builds a scalable, centralized notification and activity tracking infrastructure for EventOne, utilizing real-time Socket.IO communication, unread state sync, and a premium organizer dashboard activity log feed.

Key Changes

• Database & Services: Added the ActivityLog mongoose schema with 90-day TTL and a centralized logger service (logActivity).
• Realtime Unread Sync: Realtime unread count updates via socket when notifications are created, deleted, or marked read.
• Organizer Activity Timeline: Exposed /api/events/activities/organizer route and created a sleek vertical timeline tab on the organizer dashboard.
• Realtime Event Broadcasts: Dashboard instantly pulls and displays new activities in real-time.
• Robust Debugging & Cleanup: Fixed multiple frontend reference and scoping bugs in CustomerDashboard.jsx, SocketContext.jsx, and CoOrganizerPanel.jsx.

🔗 Related Issue
Closes #387

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[github-actions]

❌ PR Format Check — Failed — Please Fix Below

Hi @saidai-bhuvanesh! Please fix the issues below before your PR can proceed to mentor review.

❌ Must Fix Before Proceeding

❌ Issue #387 is not assigned to you (@saidai-bhuvanesh) — You must be assigned to the issue before submitting a PR.

Comment /assign on Issue #387 or ask a maintainer to assign it to you.

⚠️ Warnings (recommended)

⚠️ No testing steps mentioned — Add how reviewers can verify your changes

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