feat(ui): notify open tabs when a new server version is deployed (reload prompt) #614

Problem

After a deploy, a tab that was already open keeps running the old JavaScript until the user reloads. New features look missing (seen after v0.2.6: the RX 1h column on Observers only appeared after a manual refresh), and an old client can disagree with the new API shape.

Proposal

Show a small, non-blocking "New version available – reload" notice when the server's build changes while a tab is open.

• Signal. /api/health already reports {version, commit, buildTime} (used in public/nav-drawer.js). Remember the commit seen at page load. The __BUST__ value in index.html is another option.
• When to check (no extra polling load). Piggyback on what already happens:
  • when the tab becomes visible (visibilitychange);
  • when the WebSocket reconnects, since a deploy restarts the server;
  • at most once every few minutes otherwise.
    No per-packet or per-render calls.
• UI. A dismissible banner or toast with a Reload button, styled with CSS variables (theme-aware) and accessible (role="status", keyboard reachable). It must never auto-reload, so nobody loses filters or an open detail pane.
• Edge cases.
  • Ignore failed or 5xx health responses during the restart window.
  • Show the notice only once per new commit.
  • Do not show it on first load.

Tests

• Unit tests (vm.createContext):
  • the compare/notify logic, including that a missing or failed health response does not notify;
  • the same commit does not notify;
  • a new commit notifies once;
  • dismiss is respected.
• Playwright: stub /api/health to change the commit, fire visibilitychange, assert the banner appears, and assert that Reload reloads.

Config / customizer

The check interval can be hardcoded at first. Note it for the customizer later (AGENTS rule 8).