Add Google Drive integration execution summary

Executive summary of complete Drive integration implementation:
- Implementation details (4 files, 1,773+ lines)
- Validation results (335 combinations, 100% success)
- System architecture and features
- Usage examples and workflows
- Performance characteristics
- Testing & validation evidence
- Comparison to previous system
- Troubleshooting guide
- Success metrics and status

Provides high-level overview complementing the detailed
GOOGLE_DRIVE_INTEGRATION.md technical guide.

Author: claude