Follow-up to #50238/#50381. The restart-loop is now SAFE (marker + launch
gate), but the trigger that lured users into relaunching mid-update remained:
on the in-app update hand-off the desktop window vanished almost immediately
(app.quit() 600ms after spawning the detached updater), before the updater's
own window appeared — a blank-screen gap that looks like a crash.
- Linger on the update overlay for UPDATE_HANDOFF_DWELL_MS (2.5s, was 600ms)
before quitting, on BOTH hand-off paths (in-app update + Windows bootstrap
recovery), so the message lands and bridges to the updater window.
- Strengthen the restart-stage copy and the overlay's applyingBody/applyingClose
to explicitly tell the user the window will reopen automatically and NOT to
reopen Hermes themselves while it updates. All four locales (en/ja/zh/zh-hant)
updated in parity.
Pure UX; does not touch the #50381 marker/gate mutual-exclusion safety net.
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