Mirror the screen into browser history via SvelteKit shallow routing
(pushState/replaceState with page.state) so Back/Forward move between
screens while the URL stays at /game/. Overlays (game, lobby-create) push;
lobby/login replace. A popstate→page.state effect syncs the store back
without re-pushing (no loop); the boot stamp puts a restored overlay above
the load entry so Back falls through to lobby. In-game view switches never
touch history.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Add `appScreen` + `activeView` rune singletons with a shared sessionStorage
snapshot — the in-memory source of truth that replaces URL-based screen/view
routing for the single-URL app-shell. Not wired in yet (additive).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Ilia Denisov