refactor(ci): implement proper diagnostic collection and remove logs from repo

Major improvements to CI diagnostic handling:

## Removed CI Logs from Repository
- Deleted all .claude/CI_error/ logs (130+ files)
- These logs should never be committed to the repository
- Added comprehensive .gitignore entries to prevent future commits

## Enhanced CI Diagnostic Collection
- Added automatic diagnostic collection on test failure
- Collects environment info, test results, and system diagnostics
- Separate implementations for Unix and Windows runners
- All diagnostics uploaded as GitHub Actions artifacts

## Documentation
- Created docs/CI_DIAGNOSTICS.md with complete guide
- Explains diagnostic collection strategy
- Provides access instructions and best practices
- Includes security considerations and maintenance guidelines

## Workflow Improvements
- Diagnostics collected in ci-diagnostics/ directory
- Artifacts retained for 30 days (configurable)
- Cross-platform support with proper error handling
- Non-blocking collection (continue-on-error: true)

This ensures debugging information is available without repository pollution.

Fixes #89

🤖 Generated with Claude Code

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

Author: thc1006