feat(orchestrator): scan execution path

[macroflux]

Summary

Tasks

• Extend orchestrator /execute to support 'scan'
• Invoke Sensor Bus → get ultrasonic frame
• Run occupancy.build_grid
• Emit telemetry event: occ_grid_built with grid size + count.

Acceptance

E2E test passes; telemetry JSONL contains occ_grid_built.

Area

orchestrator

Priority

medium