Remove migration-related documentation files from git tracking

Removed from git (but kept locally):
- IMPLEMENTATION_PLAN.md
- MIGRATION_PLAN.md
- test_baseline.txt
- test_results_after_fixes.txt
- test_results_phase8.txt

These files were useful during the migration but don't need to be tracked in git.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: twiecki