Fix: AI Request Logs header overlap and sticky positioning

[Infinite-Null]

Closes #704

Summary

This PR fixes a visual overlap issue in the AI Request Logs screen where the table header appear above the sticky page header while scrolling.

Additionally, it updates the sticky header positioning to account for the WordPress admin bar height, ensuring the header remains correctly positioned across different admin layouts.

What Changed

• Added a z-index to the AI Request Logs page header to ensure it remains above the table header.
• Updated the sticky header top offset to use the WordPress admin bar height CSS variable.

Testing Instructions

1. Navigate to AI Request Logs (/wp-admin/tools.php?page=ai-request-logs).
2. Ensure there are enough log entries to make the page scrollable.
3. Scroll through the logs.
4. Verify that:
   • The page header remains above the table header.
   • The page header does not overlap with the WordPress admin bar.
   • The header positioning behaves correctly while scrolling.

Screenshots

Before	After

Screencast

Before

Screen.Recording.2026-06-12.at.11.31.21.AM.mov

After

Screen.Recording.2026-06-12.at.11.25.55.AM.mov

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Co-authored-by: Infinite-Null <ankitkumarshah@git.wordpress.org>

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