Fix PDF viewer issues, optimize downloads, improve sidebar behavior, and add reusable announcement component

[Rithish-2914]

Purpose

This PR resolves multiple issues related to the PDF viewer, download performance, sidebar behavior, and code quality. It also introduces a reusable announcement component with documentation to improve maintainability and future extensibility.

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Corresponding issues

Closes #463
Closes #498
Closes #474
Closes #476

Addresses #461 (issue no longer exists and can be closed if required).

Closes #454

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Showcase

• PDF now starts on the correct page during the initial render.
• Scroll position resets whenever the PDF page changes.
• Sidebar sticky behavior is more consistent.
• Faster downloads when multiple papers are downloaded as a ZIP.
• New reusable announcement component for advertisements.

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Changes

• Fixed the PDF viewer rendering the first page as page 0.
• Reset the scroll position after every PDF page change.
• Improved the sticky behavior of the sidebar.
• Optimized ZIP generation and download flow for multiple papers.
• Removed the unnecessary useEffect from CatalogueContent.
• Created a reusable Announcements.tsx component for advertisements across the Papers platform.
• Added inline comments to improve readability and maintainability.
• Added supporting documentation for the announcement component.

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Additional Notes

• No breaking changes.
• Existing functionality remains unaffected.
• Performance improvements have been made for bulk downloads.
• The reusable announcement component is documented for future contributors.

Announcement Component Documentation:
https://docs.google.com/document/d/17kfLUMBDCu6PhcDLx-qtu0C9ZNAshpCSyLsrHHgalM0/edit?usp=sharing