chore: remove internal development files and test data

- Removed internal docs: WORKLOG, PLAN, HOMEBREW_TAP_SETUP, PUBLISH_GUIDE, SELF_TESTS, TEST_REPORT
- Removed duplicate files: CHANGELOG (use RELEASE_NOTES), CONTRIBUTING.md (use wiki version)
- Removed test data: examples/, test_files/, test_inputs/, make_samples.py
- Updated scripts/self_test.py to work without test_files directory
- Updated wiki/Contributing.md to remove references to deleted files

Author: kiku-jw