fix(serve): the run list notices a run appearing or disappearing

[skakri]

refresh() is the only thing that reads the run list, and it ran once per project selection plus once when the dashboard itself started a run:

useEffect(() => { void refresh(); }, [refresh]);   // refresh changes only when project does

Every other way the set changes went unnoticed. A run started with ratatoskr run in a terminal never appeared; a run deleted by ratatoskr runs rm stayed on screen indefinitely. A reload or a project switch was the only cure, which is easy to miss because the dashboard otherwise looks live — the event stream keeps updating the run you are already on.

Polled, not streamed

There is no event for "the set of runs changed". The per-run stream only exists once you know a run to subscribe to, which is exactly the thing being missed, so a stream cannot carry the first news of a run.

Ten seconds, and only while the tab is visible, with an immediate read on becoming visible again. A backgrounded dashboard costs nothing, and coming back to one shows the current set at once rather than after the next tick — which is the common case, since the reason the set changed is usually something you just did in a terminal.

The selection, too

refresh kept the current runId unconditionally. Deleting the selected run therefore removed its row from the list while the detail pane went on showing it — a run that no longer exists, rendered as though it did. It now keeps a selection that is still in the list and falls back to the newest when it is not.

Verified

Driven with a browser held open across the change, rather than asserted about the code: 74 rows on load, one run deleted from a terminal, 73 rows fourteen seconds later, no reload. Before this, it stayed at 74.

bun run typecheck passes. cargo fmt, cargo clippy --workspace --all-targets -D warnings and cargo test --workspace are green — no Rust changed, but the dashboard ships from this workspace.

Note there is no unit test: web/ has no test runner, so a test file there only gates typecheck and never executes. The browser check above is the verification.