feat(ultrawork-manifesto-web): add favicon, og-image, and multi-language support

- Add favicon.png and og-image.png with custom designs
- Add og:image meta tags with dimensions and alt text
- Create localized versions: Korean, Japanese, Chinese, Spanish
- Update styles with language selector and responsive design

ultrawork-manifesto-web/src/index.html

@@ -10,8 +10,16 @@
     <meta name="keywords" content="ultrawork, developer productivity, AI engineering, deep work, tech manifesto, oh my opencode, sisyphus">
     <meta name="robots" content="index, follow, max-image-preview:large">
     <link rel="canonical" href="https://ulw.dev/">
+    <link rel="alternate" hreflang="en" href="https://ulw.dev/">
+    <link rel="alternate" hreflang="ko" href="https://ulw.dev/ko/">
+    <link rel="alternate" hreflang="ja" href="https://ulw.dev/ja/">
+    <link rel="alternate" hreflang="zh" href="https://ulw.dev/zh/">
+    <link rel="alternate" hreflang="es" href="https://ulw.dev/es/">
+    <link rel="alternate" hreflang="x-default" href="https://ulw.dev/">
     <meta name="theme-color" content="#0a0a0a">
     <meta name="author" content="Yeongyu Kim">
+    <link rel="icon" type="image/png" href="./images/favicon.png">
+    <link rel="apple-touch-icon" href="./images/favicon.png">
     
     <!-- Open Graph / Facebook -->
     <meta property="og:type" content="website">
@@ -164,7 +172,7 @@
                 <div class="approach prometheus-approach">
                     <h3>Approach 2: Prometheus + Atlas</h3>
                     <p class="approach-tagline">When you want strategic control.</p>
-                    <p>You say: <code>프로메테우스 에이전트 add authentication</code></p>
+                    <p>Press <kbd>Tab</kbd> to switch agents, then: <code>add authentication</code></p>
                     <p><strong>Prometheus</strong> (Strategic Planner):</p>
                     <ul>
                         <li>Conducts deep codebase research via parallel agents</li>
@@ -316,6 +324,17 @@ Human Intent → Agent Execution → Verified Result
                 Get Oh My OpenCode →
             </a>
             <p><strong>just ulw ulw</strong></p>
+            
+            <nav class="language-selector" aria-label="Language selection">
+                <span class="language-selector-label">Language</span>
+                <div class="language-links">
+                    <a href="/" class="language-link active" lang="en">English</a>
+                    <a href="/ko/" class="language-link" lang="ko">한국어</a>
+                    <a href="/ja/" class="language-link" lang="ja">日本語</a>
+                    <a href="/zh/" class="language-link" lang="zh">简体中文</a>
+                    <a href="/es/" class="language-link" lang="es">Español</a>
+                </div>
+            </nav>
         </div>
     </footer>
 </body>