fix(core): make built-in plugin fallback robust and use it for demo generation via hey-openapi\n\n- Correct fallback path to dist src/index.js and support CJS require + file URL import\n- Switch demo target to 'hey-openapi' with a valid client option\n- Add @hey-api/openapi-ts to workspace devDependencies to enable runtime codegen

Author: Mac Mini

apps/demo/project.json

@@ -30,10 +30,11 @@
     "generate-api-with-core": {
       "executor": "@nx-plugin-openapi/core:generate-api",
       "options": {
+        "generator": "hey-openapi",
         "inputSpec": "apps/demo/swagger.json",
         "outputPath": "apps/demo/src/app/api-core",
         "generatorOptions": {
-          "skipValidateSpec": true
+          "client": "fetch"
         }
       },
       "outputs": ["{options.outputPath}"]