Wire broadcastStreamWatch (LiveKit data-channel ping) to all three
explicit user-action sites in StreamTile: "Stop Watching" context-menu
item, "Watch Stream" context-menu item, and the handleWatch button
callback. Broadcast is intentionally confined to click sites only —
not wired in voiceStore actions — to prevent noisy stream_user_left
sounds on automatic teardown paths in useLiveKit.ts.