fix(auth): drop the stored token before redirecting to login

[davidsu]

redirectToLogin() navigated to /login while leaving the rejected token in localStorage. Apps that serve their own login page then boot again with the same dead token, get another 401, and redirect to /login forever — the loop that hit ~3k custom-auth apps when the legacy app-user signing key was cut off (https://base44workspace.slack.com/archives/C095K108GKU/p1787509962872049).

The storage clear that logout() already does is extracted into a helper and redirectToLogin() calls it before navigating. Apps pick this up on their next build/publish; the installed population is covered server-side by base44-dev/apper#21743.

[github-actions]

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