Suggested Python submission layout

The grader requires only the top-level Makefile ABI and runtime network contract. Internal layout may differ.

student-project/
├── Makefile
├── scripts/
│   └── run.sh
├── hub.py
├── rosbridge_server.py
├── arm_sim_node.py
├── kinematics.py
├── ik_node.py
├── ik_action_node.py
├── ik_trial_node.py
└── arm_lib/
    ├── __init__.py
    ├── internal.py
    ├── arm_dynamics.py
    ├── integrators.py
    ├── pid.py
    └── expr.py

Standard library only. scripts/run.sh must read ARM_SIM_LINKS (default 2) to select link count.