When updates complete quickly, the status API may return 'completed' before
the frontend detects the 'restarting' phase. This left users staring at a
frozen modal with no feedback, requiring manual page refresh.
Changes:
- When status is 'completed', immediately check /api/health
- If backend is healthy, reload the page to get new version
- If health check fails, assume restart in progress and start health polling
- Ensures users always get reloaded to the new version automatically
This fixes the UX issue reported in discussion #628 where the update modal
appeared frozen indefinitely despite successful update completion.
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