Folding a phone on the home screen left the welcome screen up when the page
had loaded wide (#702): the phone overview's breakpoint listener was wired
from its first show, which a wide-loaded page never reaches. Both home
screens' breakpoint listeners are now installed once from init() and act
only while a home surface is up.
A rail render queued just before the fold could also unhide the desktop
rail behind the phone overview; the debounced refresh now asks again when
it fires.
Tests: test/home-breakpoint-listeners.test.ts (gate) and
test/home-breakpoint-swap.browser.test.ts (browser suite: wide-first and
narrow-first across 599/600 and 767/768, plus a height-only resize).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
