Wiki: Create Spoke Page for Core - MMTk-Bindings

### Goal
Document the bridge between JNode and MMTk.

### Instructions
1. **Use the Skill:** Apply the `update-wiki` skill.
2. **Research:** Analyze `core/src/mmtk-vm/` and GC registration logic.
3. **Content:** Explain how the VM provides the required 'Plan' and 'Space' definitions to MMTk.