XY-700: Lane control P0: make dashboard active-lane controls observe-only

[yvette-carlisle]

Summary

• Remove dashboard active-lane stop/interrupt UI and click dispatch.
• Stop advertising and accepting dashboard WebSocket lane/project mutation actions while preserving subscribe/focus/ack and account selection controls.
• Update focused dashboard tests and operator-control-plane docs for the observe-only active-lane mutation boundary.

Verification

• cargo make fmt
• cargo make lint-fix
• cargo make test
• git diff --check
• semantic drift audit: pass