Explain sign-in and sign-up errors in plain words

Supabase's raw messages ("email rate limit exceeded", "Invalid login
credentials") left people stuck. The auth dialog now says what happened and
what to do: wait out the per-address cooldown, try again later or use Google
when the project's email limit is hit, check the password, confirm the email.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Update live link in README for GitHub Pages