build(mobile): declare App platform compiler to stop build:app false green

`@dcloudio/uni-app-plus` was never declared, so `uni build -p app` silently
fell back to an H5 shell: exit code 0, `DONE Build complete.`, but the output
was only `index.html` (still carrying the `/h5/assets/...` base path) with no
`app-service.js`, `app-renderjs.js` or `manifest.json`. Because
`docs/MOBILE_APP_PACKAGING.md` lists that command as a local verification
step, App platform code was reported as built without ever reaching the App
compiler.

Declare the compiler at the same version as the other `@dcloudio` packages,
guard the version alignment in `tests/app-packaging.test.mjs`, and document
that success is judged by the emitted artifacts, not by the DONE line.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

mobile-uni/tests/app-packaging.test.mjs

@@ -1,10 +1,12 @@
 import assert from 'node:assert/strict';
 import { execFileSync } from 'node:child_process';
+import { readFile } from 'node:fs/promises';
 import { test } from 'node:test';
 import { fileURLToPath } from 'node:url';
 import { dirname, resolve } from 'node:path';
 
 const mobileRoot = resolve(dirname(fileURLToPath(import.meta.url)), '..');
+const readJson = async (path) => JSON.parse(await readFile(new URL(path, import.meta.url), 'utf8'));
 
 test('App 图标与启动图映射均可由预检脚本验证', () => {
   const output = execFileSync(process.execPath, ['scripts/verify-app-assets.mjs'], {
@@ -13,3 +15,15 @@ test('App 图标与启动图映射均可由预检脚本验证', () => {
   });
   assert.match(output, /App asset verification passed/);
 });
+
+// 缺少 App 平台编译器时 `uni build -p app` 不会报错，只会静默产出带 /h5/ 基路径的
+// H5 空壳（无 app-service.js/app-renderjs.js），使 build:app 成为假绿，renderjs
+// 实时对练代码实际从未被 App 编译器处理。
+test('App 平台编译器已声明且与其他 uni 包同版本，避免 build:app 静默回落 H5', async () => {
+  const pkg = await readJson('../package.json');
+  const appPlus = pkg.dependencies?.['@dcloudio/uni-app-plus'];
+
+  assert.ok(appPlus, '缺少 @dcloudio/uni-app-plus，build:app 会静默产出 H5 空壳');
+  assert.equal(appPlus, pkg.dependencies['@dcloudio/uni-app']);
+  assert.equal(appPlus, pkg.devDependencies['@dcloudio/vite-plugin-uni']);
+});