Loader (cms-client.js), submodule-aware editor source path, build:watch

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

package.json

@@ -7,7 +7,8 @@
   "scripts": {
     "dev": "vite",
     "dev:mock": "CMS_MODE=mock vite",
-    "build": "tsc --noEmit && vite build --mode lib",
+    "build": "tsc --noEmit && vite build --mode lib && vite build --mode loader",
+    "build:watch": "vite build --mode lib --watch & vite build --mode loader --watch & wait",
     "preview": "vite preview",
     "typecheck": "tsc --noEmit",
     "test": "vitest run",