A live Inbox: server push, heartbeat and tab title #818

Parent

#776

What to build

The Inbox stays current by itself.

• The push stream: one server-push stream tells the page that Commands changed, and the page re-renders with an idiomorph morph. The selection and fold state survive.
• Polling: when the stream drops, the page checks again at intervals.
• The heartbeat dot: it beats when a Run's log grows, using growth the server sees, and lies flat while the Run is Silent.
• The tab title: it reads "‹n› need you", and the favicon gets a dot when something in Needs you is urgent.
• New since you last looked: rows that are new since the last visit are marked, remembered per browser.

Acceptance criteria

• Starting, advancing or ending a fixture Command pushes an event, and the Inbox morphs without a reload or a jump in the selection.
• With the stream cut, the page polls and catches up.
• The heartbeat reflects log growth, and is flat for a Silent Run.
• The tab title and favicon dot follow Needs you.
• "New since you last looked" works from browser storage, and nothing breaks without it.
• Tested over HTTP for the stream's events, and with Playwright for the morph keeping the selection.