refactor: replace intersection observer in board

[Schwehn42]

Description

Replaces the intersection observer used to determine whether the board is scrollable and which column to show. Reasons:

1. this is part of a larger refactor of the board and column component
2. the code was clunky
3. using a hook is more readable and reusable
4. the tests wouldn't work with a higher TS version so not requiring them keeps us out of trouble

Changelog

• add hook useIsTouchingSides
• remove IntersectionObserver and all surrounding logic from Board
• change board scroll logic

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• The application was tested in the most commonly used browsers (e.g. Chrome, Firefox, Safari)

[github-actions]

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[octomind-dev]

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Test Report: 14/14 successful.

description	status	details
About Section Visibility Test	Passed ✅	click
change avatar	Passed ✅	click
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close cookie banner - front page	Passed ✅	click
close cookie banner - sign-in	Passed ✅	click
create and delete board columns	Passed ✅	click
create_and_delete_notes_and_actions_v2	Passed ✅	click
create lean coffee board	Passed ✅	click
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commit sha: e8f9af6