feat(config-editor): extension entry + minimal Vue panel proving end-to-end IPC

Task 12 of plan 2026-06-20-config-editor-foundation. Adds:
- src/main/index.ts: onLoad + message handlers (return value = request resolve,
  per Cocos 3.x verified IPC mechanism; fallback note left in plan)
- src/panels/default/{index,app}.ts: Editor.Panel.define host + Vue 3 minimal
  app (table switcher, key list, record JSON dump)
- static/template/default/index.html + static/style/default/index.css

Deviation from plan (necessary, flagged): esbuild.config.mjs now marks
node:fs/node:path as external for the panel entry (platform:'browser').
The plan's panel reads static template/style at runtime via Node fs, which
requires these builtins; Cocos panel runs in an Electron renderer that
provides them. Without this, esbuild errors with 'Could not resolve node:fs'.

Build verified: dist/main.js (9.5mb, typescript compiler API bundled) and
dist/panels/default.js (628kb, vue.esm-bundler bundled) both generate.

extensions/pixelhero-config-editor/esbuild.config.mjs

@@ -11,9 +11,12 @@ const common = {
   alias: { 'vue': 'vue/dist/vue.esm-bundler.js' },
 };
 
+// 面板进程在 Cocos 的 Electron 渲染层运行，可访问 Node 内建（fs/path），但 vue 必须
+// 打进浏览器侧 IIFE。因此面板项用 platform:'browser' + 把 node: 内建标为 external，
+// 交由运行时解析；这样 esbuild 既不抱怨，又保持 plan 的"运行时读 static 文件"语义。
 const entries = [
   { entryPoints: ['src/main/index.ts'], outfile: 'dist/main.js', platform: 'node', format: 'cjs', external: [] },
-  { entryPoints: ['src/panels/default/index.ts'], outfile: 'dist/panels/default.js', platform: 'browser', format: 'iife', external: [] },
+  { entryPoints: ['src/panels/default/index.ts'], outfile: 'dist/panels/default.js', platform: 'browser', format: 'iife', external: ['node:fs', 'node:path'] },
 ];
 
 if (watch) {