#1423 Refactor background.js: Automate Push Subscription & Improve Notification Handling

[Anonymous]

Originally created by: GAURAVCHAWLA1808

This PR addresses the review feedback from PR [#1410] by isolating and implementing the requested changes separately. It focuses specifically on automating the push subscription process and improving notification handling in background.js.

Changes Implemented:
background.js:

Automated Push Subscription:
The extension now automatically subscribes users to push notifications when installed or updated.
Prevents redundant subscriptions by checking for existing subscriptions before subscribing.
Improved Notification Handling:
Push events now properly extract and display notification data, including title, message, and icon.
Ensures notifications open relevant URLs when clicked using notificationclick event handling.
Enhanced Logging & Debugging:
Added detailed logs to track subscription status, push event reception, and notification interactions.
Improved error handling for failed subscriptions to ensure smooth debugging.
This ensures a more structured and modular approach, making the review process smoother and enhancing the extension's push notification functionality.

Fixes Complete web push example with non-interactive subscription [#1408]