Add APK download button to GitHub Pages site

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: friuns

docs/index.html

@@ -91,7 +91,8 @@ <h1><span class="emoji">🤖</span> Codex App Android</h1>
     <span class="badge"><span class="dot blue"></span> Node.js 24 + Vue 3</span>
   </div>
   <div class="cta-row">
-    <a href="https://github.com/friuns2/codex-app-android" class="cta cta-primary">⭐ View on GitHub</a>
+    <a href="https://github.com/friuns2/codex-app-android/releases/latest/download/codexapp.apk" class="cta cta-primary">📥 Download APK</a>
+    <a href="https://github.com/friuns2/codex-app-android" class="cta cta-secondary">⭐ View on GitHub</a>
     <a href="https://github.com/friuns2/codex-app-android#-quick-start" class="cta cta-secondary">⚡ Quick Start</a>
   </div>
 </div>