.mindmodel content files end with yaml but should be md

## Description

while creating a mindmodel with /mindmodel the content files are ending with yaml but should be md. 

## Steps to Reproduce

1. Set up open code with qwen3.6 35b
2. run /mindmodel
3. get wrong file endings

## Environment

- **Package version**: 0.10.0
- **OS**: Mac Tahoe
