CHANGES:
* Return summary text from `ParseFileChanges` separately.
* Update `chatter` to use returned summary text.
* Update tests to match new function signature.
## CHANGES
- Add FileChangesMarker constant for file changes section
- Update parser to use new constant marker
- Improve error messages with dynamic marker reference
- Update tests to use new marker format
- Update system documentation with new marker syntax
CHANGES:
- Replace deprecated io/ioutil with modern alternatives
- Add file change parsing and validation system
- Create secure file application mechanism
- Update chatter to process AI file changes
- Improve create_coding_feature pattern documentation