fix: monitor GEAR-Sonic keyboard speed

[MiaoDX]

Summary

• add live velocity monitor output for GEAR-Sonic keyboard/demo runs, including simulated-time vs wall-time tracking and support-band state
• align GEAR-Sonic planner command mapping with official slow-walk/walk/run speed bands while preserving requested target_vel
• expose inferred planner mode/target in live monitor and report/replay frames
• document the speed monitor and preserve the refactor gate/evidence log

Verification

• make toolchain
• make build
• make check
• cargo test -p robowbc-ort gear_sonic_planner_command
• cargo test -p robowbc-cli planner_status
• cargo test -p robowbc-cli velocity_monitor_collects_without_report_capture
• make test
• make clippy
• make fmt-check
• local MuJoCo smoke run confirmed planner_mode=slow_walk, planner_target=0.60 m/s appears in the live monitor

Notes

• Existing scratch artifacts .tmp/ and MUJOCO_LOG.TXT are intentionally not included.