feat: enhance Milkdown editor and file system functionality

- Normalize line endings in Markdown export for DOCX files.
- Improve selection serialization to Markdown with better handling of empty documents.
- Add a new `updateFile` function to the file system for updating file properties.
- Introduce video transcoding capabilities using FFmpeg, supporting various video formats.
- Update AGENTS.md for clearer plugin structure and responsibilities.
- Add scoped styles for TreeNodeItem component to improve UI consistency.
- Implement cross-origin isolation headers in Vite configuration for enhanced security.
- Remove obsolete test_cross.py file.

src/views/DocsView.vue

@@ -120,7 +120,7 @@ function closeConfirm() {
       </aside>
 
       <section class="docs-main">
-        <header class="docs-toolbar">
+        <header v-if="selectedNode?.type !== 'file'" class="docs-toolbar">
           <div class="toolbar-left">
             <button
               class="sidebar-toggle"
@@ -166,7 +166,10 @@ function closeConfirm() {
           :root-nodes="fs.tree.value"
           :get-file-icon="fs.getFileIcon"
           :get-file-blob="fs.getFileBlob"
+          :update-file="fs.updateFile"
+          :show-sidebar-toggle="selectedNode?.type === 'file'"
           @navigate="fs.select"
+          @toggle-sidebar="sidebarCollapsed = !sidebarCollapsed"
         />
       </section>
     </div>