Remove board recruitment page

[grahamgilbert]

No description provided.

[Copilot]

Pull Request Overview

Removes the expired "Join the Board" recruitment content from the site. Cleans up navigation and README to eliminate dead/dated references.

• Remove obsolete board recruitment page
• Remove corresponding navigation entry
• Remove related section from README

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
join-the-board.md	Deleted outdated board recruitment page
_config.yml	Removed navigation link to deleted page
README.md	Removed section referencing deleted page

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