tri harness: measure a page signed in, sessionStorage included (--save-state / --storage-state) #5848

Problem

tri harness (#5827, PR #5828) measures every width as a fresh, signed-out visitor. On app.t27.ai/game/browser the BROWSER view, signed out, is one sentence and one button: the chat and the browser itself are behind the sign-in, so the page the Queen board loop is building is the one part the harness cannot see.

Loading a Playwright storage state is not enough. app.t27.ai keeps its sign-in in sessionStorage (trinity.app.session.access / trinity.app.session.expires-at, gHashTag/trinity apps/website/src/lib/appSessionIdentity.ts), and Playwright's storage state carries cookies, localStorage and IndexedDB, not sessionStorage. A naive --storage-state would measure the signed-out page and report it under the signed-in name.

Wanted

• tri harness --save-state FILE URL: a visible browser with a temporary profile; the person signs in there themselves; Enter writes FILE with mode 600, sessionStorage included. Never overwrites; writes nothing if the session holds nothing for the URL's host.
• tri harness --storage-state FILE URL: FILE loaded read-only into each width; sessionStorage put back before page scripts, only into its own origin. Refuses (exit 2) a FILE readable by others, and one that holds nothing live for the host (another site's, or all cookies expired).
• Values never printed. Without --wait-for on a signed-in-only selector, the report says the sign-in was not established.

Refs #5827