Move plan docs to notes/ and remove ephemeral test files from repo root

Move reference docs to notes/ (alongside existing similar files):
- IMPLEMENTATION_SUMMARY.md → notes/
- VERIFICATION_GUIDE.md → notes/
- CM4AI_COMPARISON.md → notes/

Remove one-time test artifacts (no longer needed):
- PHASE3_TESTING_RESULTS.md
- TEST_ISSUE_SUMMARY.md
- test_github_issue_cm4ai.md (GitHub issue #109 already created)

Update internal reference path in VERIFICATION_GUIDE.md.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: realmarcin