add copy button

src/public/styles.css

···
     font-style: monospace;
 }
 
+@media (prefers-color-scheme: dark) {
+  .shiki,
+  .shiki span {
+    color: var(--shiki-dark) !important;
+    background-color: var(--shiki-dark-bg) !important;
+    font-style: var(--shiki-dark-font-style) !important;
+    font-weight: var(--shiki-dark-font-weight) !important;
+    text-decoration: var(--shiki-dark-text-decoration) !important;
+  }
+}
+
 :root {
   /* Light mode colors */
   --bg-color: white;
···
   color: rgba(115,138,148,.4)
 }
 
-@media (prefers-color-scheme: dark) {
-  .shiki,
-  .shiki span {
-    color: var(--shiki-dark) !important;
-    background-color: var(--shiki-dark-bg) !important;
-    font-style: var(--shiki-dark-font-style) !important;
-    font-weight: var(--shiki-dark-font-weight) !important;
-    text-decoration: var(--shiki-dark-text-decoration) !important;
-  }
+#copy-btn {
+  background: none;
+  border: none;
+  padding: 0;
+  color: var(--text-color-muted);
+  cursor: pointer;
+  text-decoration: none;
+  font-family: inherit;
+  font-size: inherit;
+}
+
+#copy-btn:hover {
+  text-decoration: underline;
+}
+
+#copy-btn:focus {
+  outline: 1px solid var(--accent);
 }

src/views/paste.pug

···
         | #{timeDifference(now, Date.parse(paste.createdAt))} ago ·
         | #{paste.lang} · 
         | #{paste.code.split('\n').length} loc · 
-        a(href=`/r/${paste.shortUrl}`) raw     
+        a(href=`/r/${paste.shortUrl}`) raw
+        |  · 
+        button#copy-btn(type="button" onclick="copyToClipboard()" data-code=paste.code) copy
+        |  ·
+        | #{comments.length} #{pluralize(comments.length, 'comment')}
       div.highlighted-code !{paste.highlightedCode}
       hr
 
···
           a(href="/login") login
           | to post a comment
 
-      +footer()
+      +footer()
+    script.
+      async function copyToClipboard() {
+        const copyBtn = document.getElementById('copy-btn');
+        const originalText = copyBtn.textContent;
+        
+        try {
+          const code = copyBtn.dataset.code;
+          await navigator.clipboard.writeText(code);
+          copyBtn.textContent = 'copied!';
+          copyBtn.style.color = 'var(--accent)';
+          
+          setTimeout(() => {
+            copyBtn.textContent = originalText;
+            copyBtn.style.color = '';
+          }, 1500);
+        } catch (err) {
+          console.error('Failed to copy: ', err);
+          copyBtn.textContent = 'copy failed';
+          setTimeout(() => {
+            copyBtn.textContent = originalText;
+          }, 1500);
+        }
+      }