- Rename 'Active Channels' card heading to 'Channels'
- Add showAllChannels state (default: active-only view)
- Pill toggle button switches between 'Active' (green) and 'All' (blue)
views; button label reflects the *current* view so clicking switches to
the other mode
- When active-only and all channels are inactive, show
'No active channels' hint instead of an empty list
- Add i18n keys dashboard.channels, dashboard.filter_active,
dashboard.filter_all, dashboard.no_active_channels to en, zh, tr
locales
- No backend changes; no new dependencies
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