feat: npm package v0.52.0 with cross-platform support

- Updated version to 0.52.0 for npm release
- Added npm installation instructions to README
- Updated architecture diagrams to v0.52.0
- Added npm version badge
- Configured GitHub Actions for cross-platform builds

Codex v0.48.0 - ThreeWayMerge & Enhanced Sub-Agent System

Release Highlights:
- ThreeWayMerge: Git-style 3-way merge with conflict detection
- Natural Language Agent: Intuitive 'codex agent' command
- Enhanced Sub-Agent System: Parallel execution support
- Binary: 39.34 MB optimized release
- Tests: 8/8 integration tests passing

Full release notes: RELEASE_NOTES_v0.48.0.md
Implementation log: _docs/2025-10-16_ThreeWayMerge_and_v048_Release.md