task(G1): layout data model - LayoutDefinition type, Yjs layouts map, undo-tracked CRUD in CADDocument

frontend/src/crdt/YjsDocument.ts

@@ -6,6 +6,7 @@ import * as Y from 'yjs';
 import type { CADElement, CADLayer, BlockDefinition } from '../types/cad.types';
 import type { ElementGroup } from '../tools/modification/GroupTool';
 import type { BackgroundConfig } from '../services/backgroundService';
+import type { LayoutDefinition } from '../types/cad.types';
 
 export interface YjsDocumentData {
   elements: Y.Map<CADElement>;
@@ -14,6 +15,7 @@ export interface YjsDocumentData {
   meta: Y.Map<unknown>;
   groups: Y.Map<ElementGroup>;
   bgConfig: Y.Map<BackgroundConfig>;
+  layouts: Y.Map<LayoutDefinition>; // Task G1
 }
 
 export class YjsDocument {
@@ -29,6 +31,7 @@ export class YjsDocument {
       meta: this.doc.getMap<unknown>('meta'),
       groups: this.doc.getMap<ElementGroup>('groups'),
       bgConfig: this.doc.getMap<BackgroundConfig>('bgConfig'),
+      layouts: this.doc.getMap<LayoutDefinition>('layouts'),
     };
   }
 
@@ -57,6 +60,11 @@ export class YjsDocument {
     return Array.from(this.data.bgConfig.values());
   }
 
+  /** Get all layouts as a plain array (Task G1) */
+  getLayouts(): LayoutDefinition[] {
+    return Array.from(this.data.layouts.values());
+  }
+
   /** Add or update a single element */
   setElement(el: CADElement): void {
     this.doc.transact(() => {