fix(M02): 도면 양식 저장이 빈 {} 로 덮이던 흠 — getDoc 을 await · 서버는 뼈대 없는 문서를 400 으로 거절

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0148XFUpPfpiuTjxF1EK9c95

M02_MasterTemplete/M02_MasterTemplete_UI_Main.ts

@@ -23,7 +23,7 @@ export interface Selection {
 }
 
 interface EditorHandle {
-  getDoc: () => unknown;
+  getDoc: () => unknown | Promise<unknown>;
   destroy: () => void;
 }
 
@@ -162,7 +162,7 @@ export function createMain(isAdmin: boolean): MainHandle {
     if (!sel) return;
     const at = sel;
     try {
-      const doc = editor ? editor.getDoc() : loaded;
+      const doc = editor ? await editor.getDoc() : loaded;
       const info = await saveTemplate(at.layer, at.kind, at.name, at.projectId, version, doc);
       version = info.판;
       loaded = doc;