Post-merge cleanup for #634 channel health diagnostics:
Backend:
- Extract health types, ClassifyChannelError, mergeChannelHealth,
buildRemediation into internal/channels/health.go
- Fix case-true anti-pattern → default in Slack config
- Remove duplicate connection-refused case in ClassifyChannelError
- Remove unused _ bool param from BaseChannel.setHealth
- Fix snapshot.Enabled == false → !snapshot.Enabled
Web UI:
- Extract channel status utilities to channels-status-utils.ts
- Extract ChannelDiagnosticsCard from channel-detail-page.tsx
- Extract ChannelAttentionPanel from system-health-card.tsx
Desktop UI:
- Extract shared getChannelStatusDisplay() to utils/channel-status.ts
- Add explicit stopped state case for visual consistency with web UI
- Add missing vi/zh locale keys for new health status states