Remove the home-page sign-in island; the hero is just "Start writing"
Drop the HandleStart handle-input CTA and its "Already have an account?" label
from the landing hero (and the now-dead handlestart styles). The home page's
only action is "Start writing → /write"; signing in happens via Publish on
/write, consistent with the rest of the flow. Retire the obsolete
_index.handlestart.test.ts CSS guard and update the landing-content guard.