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

index.html

@@ -10,17 +10,17 @@
     <meta name="theme-color" content="#0b0e14" />
     <meta name="apple-mobile-web-app-capable" content="yes" />
     <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
-    <meta name="apple-mobile-web-app-title" content="万能看图" />
+    <meta name="apple-mobile-web-app-title" content="EasyView" />
     <meta name="format-detection" content="telephone=no" />
     <link rel="icon" type="image/svg+xml" href="./icons/favicon.svg" />
     <link rel="apple-touch-icon" href="./icons/apple-touch-icon.png" />
-    <title>万能看图 · DWG/PDF 浏览器</title>
+    <title>EasyView · DWG/PDF 浏览器</title>
   </head>
   <body>
     <div id="app"></div>
     <div id="toasts" aria-live="polite" aria-atomic="false"></div>
     <div id="modal-root"></div>
-    <noscript>需要启用 JavaScript 才能使用万能看图。</noscript>
+    <noscript>需要启用 JavaScript 才能使用 EasyView。</noscript>
     <script type="module" src="/src/main.ts"></script>
   </body>
 </html>