Adds ADR-0004 documenting the architectural decision to implement centralized layout management using CRDT backing store with command pattern architecture.
## Key Technical Decisions Documented
- **Centralized State Management**: Move from scattered `node.position` mutations to single authoritative layout store
- **CRDT Foundation**: Yjs-backed store provides conflict resolution and collaboration readiness
- **Command Pattern**: All spatial mutations flow through explicit commands for undo/redo and system coordination
- **Reactive Architecture**: Transition from O(n) diff-based change detection to O(1) signal-based reactivity
## Current Architecture Problems Addressed
- Performance bottlenecks from polling-based change detection in complex workflows
- Position conflicts between LiteGraph canvas and DOMwidgets.ts overlay systems
- Inability to support collaborative editing due to direct mutation patterns
- Renderer lock-in preventing alternative rendering backends
