Fix: remove duplicate welcome file and update content

Author: MatrixCQY

src/hooks/use-file-system.ts

@@ -27,51 +27,22 @@ export interface FileSystemContextType {
   downloadFile: (id: string) => void;
 }
 
-const STORAGE_KEY = 'mathstudio-fs-v1';
-
-const INITIAL_FILES: Record<string, FileNode> = {
-  'root-welcome': {
-    id: 'root-welcome',
-    name: 'Welcome.md',
-    type: 'file',
-    parentId: null,
-    content: `# MathStudio
-
-## Features Demo
-
-### 1. LaTeX Support
-Inline: $E = mc^2$
-
-Block:
-$$
-\\int_{-\\infty}^{\\infty} e^{-x^2} dx = \\sqrt{\\pi}
-$$
-
-### 2. Code Highlighting
-\`\`\`python
-def hello():
-    print("Hello, World!")
-\`\`\`
-
-### 3. Smart Layout
-- **Split View**: Edit and preview side-by-side.
-- **Mobile Friendly**: Works great on your phone.
-
-### 4. Privacy
-- Files you create here are saved in your **browser's local storage**.
-- Visitors cannot see your private files, and you cannot see theirs.
-`,
-    createdAt: Date.now(),
-  },
-};
+const STORAGE_KEY = 'mathstudio-fs-v2';
+
+const INITIAL_FILES: Record<string, FileNode> = {};
 
 export function useFileSystem(initialPosts?: Record<string, FileNode>) {
   // Merge INITIAL_FILES with initialPosts
   const [files, setFiles] = useState<Record<string, FileNode>>(() => ({
     ...INITIAL_FILES,
     ...initialPosts,
   }));
-  const [activeFileId, setActiveFileId] = useState<string | null>('root-welcome');
+  const [activeFileId, setActiveFileId] = useState<string | null>(() => {
+    if (initialPosts && Object.keys(initialPosts).length > 0) {
+      return Object.keys(initialPosts)[0];
+    }
+    return null;
+  });
   const [mounted, setMounted] = useState(false);
 
   // Load from localStorage