Logged-in users should be redirected from /auth/login to home

[stultus]

Problem

Visiting /auth/login while already authenticated still renders the login form instead of redirecting the user away. This is confusing and lets users re-submit credentials for no reason.

Expected behavior

If the current user is already authenticated, /auth/login should redirect to the home page (search.index).

Suggested fix

At the top of the login view in app/auth/controllers.py, check current_user.is_authenticated and redirect to url_for('search.index') before rendering the form.

The same check should probably apply to /auth/signup for consistency.