docs(site): add App Store badges, SEO pages, and GSC verification

Ship official store badges on READMEs and the site, expand discoverability
with FAQ/JSON-LD/llms.txt/content pages, and add the Search Console HTML
verification file so the live Pages site can be claimed.

README.en.md

@@ -12,6 +12,12 @@ Voice input for iPhone, iPad, and Mac. Speak in any app — polished text lands
 
 [Website](https://hkgood.github.io/OSGKeyboard/) · [中文 README](./README.md) · [Privacy Policy](https://hkgood.github.io/OSGKeyboard/privacy/)
 
+<p align="center">
+  <a href="https://apps.apple.com/app/osgkeyboard/id6781553267">
+    <img src="docs/assets/badges/appstore-en.svg" alt="Download on the App Store" height="40">
+  </a>
+</p>
+
 ---
 
 ## Why OSGKeyboard
@@ -52,6 +58,14 @@ Speech is transcribed on-device by default. Polish sends **text only** — the t
 
 ---
 
+## Get the app
+
+**App Store (recommended)**
+
+<a href="https://apps.apple.com/app/osgkeyboard/id6781553267">
+  <img src="docs/assets/badges/appstore-en.svg" alt="Download on the App Store" height="40">
+</a>
+
 ## Build from source
 
 Requires macOS with **Xcode 26** and [XcodeGen](https://github.com/yonaskolb/XcodeGen).