app: live page subscribes through the bus manager

[aq1018]

PR 2 of three from docs/design/bus-manager.md. Telemetry is a fast ring subscription over the sample registers plus one read of the conversion constants; the control cluster subscribes fast to its registers inside the same span, so it costs no exchange, and writes goals, mode and torque through bus.write, where a slider burst coalesces per register. The draft clears on the first snapshot the servo answered past the burst's last write. The stream tab reads its config once and arms the burst as a command. Nothing on the Live page touches session.run or the client any more.

• telemetry-poll.ts becomes telemetry.ts: the poll loop, SampleRing and its span machinery are gone
• LatestWins and the write gap leave control.ts
• new browser spec: a burst of goal changes lands on the last one and shows coalesced in the debug readout

https://claude.ai/code/session_015YgEehU5GLftenbuhpKWMi