feat(admin): remove version checker and new version alerts

[marpisco]

No version published will have any call-backs to home, for security reasons. This update removes version alerts, and removes the version checker by Git.

This update adds the commit below. Remember to update any manuals that have still not been ported to the platform yet to remove this reference, @marpisco.

[Copilot]

Pull request overview

This PR removes the admin dashboard “new version” alert feature by deleting the Git-based version check endpoint and removing the frontend code that periodically queried it, aligning with the project goal of eliminating outbound “call-backs to home” for security.

Changes:

• Removed the admin dashboard JS/UI that displayed version/update alerts and polled every 15 minutes.
• Deleted the admin/api/version_check.php endpoint that executed git fetch and cached results in version_cache.
• Updated internal repository instructions to no longer reference the removed endpoint.

Reviewed changes

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

File	Description
admin/index.php	Removes the dashboard-only version alert container and polling script.
admin/api/version_check.php	Deletes the Git-backed version checking API endpoint entirely.
.github/copilot-instructions.md	Removes documentation/reference to version_check.php from the admin API endpoint list.