Server now parses the User-Agent header on /api/send when no explicit
source is provided, producing labels like 'iphone-safari',
'macos-chrome', 'windows-firefox' so the feed shows where messages
came from at a glance.
Browser-side peerID is now stored in localStorage instead of being
freshly random on each page load — refreshing or reopening the tab
keeps the same identity for the same browser profile.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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