Rename app to EasyView and make APK build cross-platform

- App display name -> EasyView (Android label, PWA manifest, page titles,
  about/guide text, APK artifact name)
- scripts/build-apk.mjs: auto-detect JDK/SDK/Gradle toolchain instead of
  hardcoded Windows paths; pick highest build-tools; platform 34 fallback;
  path.delimiter classpaths; npm run build without cmd.exe on POSIX
- Add build-apk.sh one-shot Linux build wrapper (loads ven env + keystore)
- Signing keystore renamed to easyview.jks (alias easyview),
  env vars EASYVIEW_KEYSTORE_PASS / EASYVIEW_KEY_PASS

vite.config.ts

@@ -16,8 +16,8 @@ export default defineConfig({
       injectRegister: false,
       includeAssets: ['icons/favicon.svg', 'icons/apple-touch-icon.png'],
       manifest: {
-        name: '万能看图 · DWG/PDF 浏览',
-        short_name: '万能看图',
+        name: 'EasyView · DWG/PDF 浏览',
+        short_name: 'EasyView',
         description:
           '手机与平板上的 DWG 图纸浏览器，支持模型空间与布局空间、图层控制、测量，以及 PDF / EPUB / XPS / CBZ / 图片阅读。',
         lang: 'zh-CN',