feat(sensor-bus): ultrasonic + imu intake

### Summary

### Tasks
- Scaffold `services/sensor-bus` FastAPI app.
- Endpoints:
  - POST /ultrasonic
  - POST /imu
- Validate against contract schemas
- Emit telemetry metrics + events
- Include `/healthz`
- Add pytest suite for 200/422.

### Acceptance
Both endpoints functional, examples validated, telemetry emitted.


### Area

sensor

### Priority

high