revert: restore GitHub + Email buttons in hero

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

css/style.css

@@ -133,14 +133,6 @@ img { max-width: 100%; display: block; }
   font-weight: 500;
 }
 
-.hero-email {
-  margin-top: 16px;
-  font-size: 0.9rem;
-  color: #888;
-}
-.hero-email a { color: #888; }
-.hero-email a:hover { color: #333; }
-
 .hero-links {
   display: flex;
   gap: 12px;

index.html

@@ -42,8 +42,8 @@
       </div>
       <div class="hero-links">
         <a href="https://github.com/tolelom" class="btn btn-primary" target="_blank" rel="noopener">GitHub</a>
+        <a href="mailto:98kimsungmin@naver.com" class="btn">Email</a>
       </div>
-      <p class="hero-email"><a href="mailto:98kimsungmin@naver.com">98kimsungmin@naver.com</a></p>
     </section>
 
     <section id="about" class="section">