feat: add duplicate snippet functionality in SnippetManager and UI

src/SnippetManager.js

@@ -157,6 +157,21 @@ export class SnippetManager {
         }
     }
 
+    duplicateSnippet(id) {
+        const snippet = this.snippets.find(s => s.id === id);
+        if (!snippet) return;
+
+        const newSnippet = {
+            ...snippet,
+            id: 'snippet-' + Date.now(),
+            name: snippet.name + ' (Copy)'
+        };
+
+        this.snippets.push(newSnippet);
+        this.saveSnippetsAndUpdateUI();
+        this.loadSnippet(newSnippet.id);
+    }
+
     saveSnippetsAndUpdateUI() {
         this.storageManager.saveSnippets(this.snippets);
         this.updateUI();

src/UIManager.js

@@ -61,6 +61,11 @@ export class UIManager {
                 this.snippetManager.deleteSnippet(snippet.id);
             }));
 
+            buttonsDiv.appendChild(this.createButton('📄', 'duplicate-snippet', (e) => {
+                e.stopPropagation();
+                this.snippetManager.duplicateSnippet(snippet.id);
+            }));
+            
             div.appendChild(buttonsDiv);
             container.appendChild(div);
         });

src/styles.css

@@ -250,3 +250,21 @@
 .snippet-item:hover .edit-snippet {
     opacity: 0.8;
 }
+
+.duplicate-snippet {
+    opacity: 0.4;
+    font-size: 14px;
+    padding: 2px 4px;
+    background: none;
+    border: none;
+    cursor: pointer;
+    min-width: 24px;
+}
+
+.duplicate-snippet:hover {
+    opacity: 1;
+}
+
+.snippet-item:hover .duplicate-snippet {
+    opacity: 0.8;
+}