docs(phase2): add comprehensive technical documentation

Add Phase 2 documentation covering:

CLI_REFERENCE.md:
- Complete command-line interface reference
- All environment variables and flags
- Usage patterns and examples
- Exit codes and error handling

ERROR_CATALOG.md:
- Comprehensive error reference
- Detection errors, version parsing, network failures
- Installation and configuration errors
- Each error includes: description, causes, solutions, examples

INTEGRATION_EXAMPLES.md:
- Programmatic API usage examples
- Single tool installation, bulk operations
- Upgrade workflows, reconciliation
- Configuration file examples
- Custom preferences and dry-run planning

TESTING.md:
- Complete testing strategy and setup
- Unit tests, integration tests, fixture management
- Coverage requirements and CI/CD integration
- Performance testing guidelines

ARCHITECTURE.md updates:
- Enhanced component descriptions
- Data flow diagrams
- Design principles and patterns
- Error handling strategies

INDEX.md updates:
- Reorganized navigation
- Quick start guides
- Phase tracking

Total addition: 3100+ lines of structured documentation
providing complete reference for developers and users.

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

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

Author: AI Assistant