ha-helios 0.12.0

Each clock can show its own dashboard. The Helios panel has one tab per paired clock; Own dashboard copies the current document into a new hidden dashboard for that clock and switches it on the spot. Every clock starts on the shared helios-clock, so nothing changes until you press the button. New admin-only WebSocket commands helios/clocks and helios/clock/set_dashboard (docs/PROTOCOL.md). No app update needed.