Real diagnostics backend for temperature, current, heartbeat, sensor health

[khuzaymahbinharis-jpg]

Context

Korede is currently unavailable. The temporary publisher in waybionic_rviz_plugins (temporary_diagnostics_publisher.py) is an interim solution for local UI validation.

Expected interface

• Topic: /diagnostics (diagnostic_msgs/msg/DiagnosticArray)
• Signal names: board.temperature, motor.current, imu.roll, imu.pitch, imu.yaw, imu.heartbeat
• Value/unit keys in DiagnosticStatus.values: value, unit

See waybionic_rviz_plugins/docs/DIAGNOSTICS_BACKEND_INTEGRATION.md on PR #2 for full mapping and acceptance criteria.

Acceptance criteria

• Publish at least 1 Hz on /diagnostics during normal operation
• Populate value and unit keys for telemetry rows
• Publish imu.heartbeat (or equivalent) for stale sensor detection
• Validate live rows in engineer_view.launch.py with use_mock_diagnostics:=false

Notes

The RViz DiagnosticsPanel should not require code changes when the real backend replaces the temporary publisher.