feat: add file download/export capability from sidebar

Author: MatrixCQY

src/components/sidebar.tsx

@@ -12,7 +12,8 @@ import {
   Edit2,
   MoreVertical,
   FilePlus,
-  FolderPlus
+  FolderPlus,
+  Download
 } from "lucide-react";
 import { cn } from "@/lib/utils";
 import { FileNode, FileSystemContextType } from "@/hooks/use-file-system";
@@ -163,6 +164,11 @@ function FileTreeNode({ node, fileSystem, depth }: FileTreeNodeProps) {
               </button>
             </>
           )}
+          {node.type === 'file' && (
+            <button onClick={handleDownload} className="p-0.5 hover:bg-background rounded" title="Download">
+              <Download size={12} />
+            </button>
+          )}
           <button onClick={handleRename} className="p-0.5 hover:bg-background rounded" title="Rename">
             <Edit2 size={12} />
           </button>

src/hooks/use-file-system.ts

@@ -188,6 +188,21 @@ export function useFileSystem() {
     );
   }, [files]);
 
+  const downloadFile = useCallback((id: string) => {
+    const node = files[id];
+    if (!node || node.type !== 'file') return;
+
+    const blob = new Blob([node.content], { type: 'text/markdown' });
+    const url = URL.createObjectURL(blob);
+    const a = document.createElement('a');
+    a.href = url;
+    a.download = node.name;
+    document.body.appendChild(a);
+    a.click();
+    document.body.removeChild(a);
+    URL.revokeObjectURL(url);
+  }, [files]);
+
   return {
     files,
     activeFileId,
@@ -199,5 +214,6 @@ export function useFileSystem() {
     selectFile,
     toggleFolder,
     searchFiles,
+    downloadFile,
   };
 }