exp(sim-bridge): ingest simulated sensor data

### Summary

### Tasks
- Create `exp/sim-bridge` Python module.
- Support UDP/WebSocket input → translate to ultrasonic.v1 + imu.v1.
- POST to Sensor Bus.
- Config via `.env` (SIM_SOURCE, SENSOR_BUS_URL, MONAD_KEY).
- Unit test with fake sender.

### Acceptance
Sensor Bus receives N frames; telemetry shows matching count.


### Area

sim

### Priority

medium