fix: publish odometer on planner topic

[lblommesteyn]

Problem
When running AP1 with the RealSense D455 bag and the mapping pipeline, UFLD publishes lanes and mapping forwards them to /ap1/mapping/lanes, but the planner never publishes /ap1/planning/target_path.

The planner log reports:

1 or more necessary field is null. Skipping loop.

The missing input is odometer. Planner defaults to subscribing to /ap1/mapping/odometer, but slam_bridge publishes cumulative distance on /ap1/localization/distance, so the planner never receives the odometer FloatStamped.

Changes

• Publish slam_bridge cumulative distance on /ap1/mapping/odometer by default.
• Update mapping_pipeline.launch.py's output_distance_topic default to match planner's odometer input.
• Update README topic references for the odometer output.

Test plan

• python3 -m py_compile mapping_localization_python/mapping_localization_python/slam_bridge_node.py
• git diff --check
• Runtime evidence from AP1 WSL/Jazzy bringup: /ap1/perception/lanes and /ap1/mapping/lanes publish from the RealSense bag, while /ap1/planning/target_path remains silent because /ap1/mapping/odometer has no publisher.