## Why

The current `docs/architecture.md` provides a basic overview of fsspeckit's domain package architecture but lacks comprehensive detail about the actual implementation, architectural decision records, integration patterns, and production deployment considerations. Users need complete technical documentation that reflects the real implementation and serves as both a reference and practical guide.

## What Changes

- **Complete Rewrite**: Transform the basic 106-line overview into a comprehensive 800+ line technical reference
- **Add Architectural Decision Records (ADRs)**: Document WHY key design choices were made (domain package structure, backend-neutral planning, façade pattern, multi-cloud abstraction)
- **Real Implementation Details**: Replace idealized descriptions with actual implementation patterns discovered in the codebase
- **Integration Patterns**: Add cross-domain integration examples showing how packages work together in practice
- **Performance & Scalability Architecture**: Document caching strategies, parallel processing, monitoring, and observability
- **Production Deployment Architecture**: Include multi-cloud deployment, security, compliance, and operational excellence patterns
- **Enhanced Visual Documentation**: Create comprehensive Mermaid diagrams showing actual data flow and component interactions
- **Extension Points Documentation**: Explain how users can extend the architecture and add new capabilities

## Impact

- **Affected specs**: This change focuses on documentation architecture rather than functional capabilities
- **Affected code**: `docs/architecture.md` (complete rewrite)
- **Documentation consistency**: Requires updates to related documentation for cross-references
- **User experience**: Dramatically improved understanding of fsspeckit architecture and practical implementation guidance
- **Development velocity**: Better architectural understanding leads to more effective feature development and troubleshooting

This is a documentation-only change that does not affect code functionality but significantly improves the technical reference quality and user understanding of the system.