Add update_channel setting (stable/canary) to Settings with UI toggle.
Stable channel uses Tauri updater plugin; canary fetches latest-canary.json
and opens GitHub release page for manual download. Add useFeatureFlag()
hook with localStorage overrides and compile-time defaults (no remote
dependencies). Add release-canary.yml CI workflow for canary branch builds.
Update stable workflow to preserve latest-canary.json on GH Pages.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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