Expose a sandbox port from the sandbox page

[vitramir]

Needs agynio/expose#37 — without it a browser cannot expose or remove a port at all.

Starting a dev server in a sandbox meant dropping into the shell, running a command, and reading the URL out of its output. Nothing on the page said what the sandbox was serving or where.

Shape

Ports live in a header chip beside the clocks, not a strip of their own. An address is derived from the sandbox, so every port shares one host — factoring it out collapses a row to its port, and the whole set then fits in the header. The terminal keeps the vertical space a second strip was taking.

The chip is present whenever the sandbox is running, reading "None" with nothing exposed. Hiding it until the first port would be cleaner and would leave nobody a way to find the feature.

Behind it, a popover: the host once, one row per port (link, copy, remove), the expose control, and the reachability notice.

The expose control is a ghost row

Two boxy controls in a popover of rows read as pasted in. At rest it matches the rows above it; clicking turns the row itself into an inline field that submits on Enter and cancels on Escape.

States worth reviewing

• Re-exposing an existing port is not an error. The service returns the record it already has, so the editor closes and that port pulses rather than an error appearing for something that worked.
• A refusal stays in the row with a retry, rather than becoming a toast that outlives the popover and detaches from what caused it.
• The empty popover drops the host line and the notice — neither says anything until there is an address.
• No live updates. Expose publishes no notification events, so a port exposed inside the shell surfaces on the next refetch: mount, the app's own mutations, or the workload changing.

57 tests, lint and typecheck clean. Deployed from source and checked in the browser.

Spec: agynio/architecture#179 (merged).