OR-264 feat: "Restart now" button on the update banner

[myles332]

Summary

The "Updated to X. Restart to use it." banner (and the Settings → Updates card) now have a Restart now button that relaunches OpenResearch into the installed version.

• POST /api/update/restart (409 unless a newer copy is installed) answers, then signals the serve loop; after the usual harness shutdown the process relaunches.
• Terminal orx up execs itself: same PID, terminal, and port, with --no-browser added so the reloading tab is the only one.
• macOS app: a detached shell waits for the old process to exit, then open -n --env ORX_APP_RELAUNCH_PORT=<port> the bundle; the app reuses that port (if free) and skips opening a browser.
• The dashboard polls /api/update until a different server instance answers, then reloads so the UI is the new build. Timeout after 60s shows a by-hand message.
• The banner now also renders on the zero-projects Projects screen, which previously omitted it.
• UpdateStatus gains canRestart (platform support) and instance (per-process id). The route is on the remote-workspace forbidden list like the other update routes.

Testing

• cargo fmt --all --check, cargo clippy --all-targets -D warnings, cargo build --locked, cargo test --locked (723 passed)
• UI: i18n lint, paraglide compile, tsc --noEmit, style lint, vite build; ui/dist regenerated
• Terminal path end to end on an isolated dev slot with a simulated installed version: POST answered, same PID came back on the same port, log shows the restart line and a fresh startup
• Real installer-channel update on macOS: click Restart now, tab reloads on the new version, no second tab
• Real installer-channel update on Linux (binary replaced, (deleted) path)
• macOS app bundle: click Restart now, app relaunches on the same port, existing tab reloads, no second tab
• Banner and Settings card rendered and the button exercised in the browser on a dev slot (restart, reload, new server instance)
• Settings → Updates card button behaves the same and locks the other controls while restarting

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