fix: Redirect to login page if profile element is missing

[boomzero]

What does this PR aim to accomplish?:

This pull request introduces a change to improve user experience by redirecting users to the login page if they are not logged in.
This closes #286.

How does this PR accomplish the above?:

• Added a check to determine if the #profile element is present on the page. If it is not found, the user is redirected to the login page at https://www.xmoj.tech/loginpage.php. (XMOJ.user.js, XMOJ.user.jsR562-R564)

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