Initialize and manage sticky footer

[tmrr13]

Improve footer slide behavior when dragging the scrollbar.

The previous implementation did not correctly handle revealing/hiding the footer when a user dragged the scrollbar, especially when near the bottom of the page. This fix introduces wasAtBottom and isNearBottom states to provide a more robust and intuitive interaction, preventing premature hiding and allowing proper interaction when scrolling from the bottom.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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