feat: Implement sidebar collapse and expand functionality

- Add CSS for collapsed sidebar state and transitions
- Introduce SidebarToggle class for managing collapse/expand logic
- Integrate SidebarToggle initialization in main script
- Add toggle button to navbar and make mini sidebar clickable
- Store sidebar collapsed state in localStorage
- Filter image files and directories in view mode via FileTree
- Make navbar brand clickable to navigate to collection root or home

templates/index.html

@@ -30,10 +30,18 @@
     <!-- Navbar -->
     <nav class="navbar navbar-expand-lg">
         <div class="container-fluid">
-            <!-- Left: Logo and Title -->
-            <span class="navbar-brand mb-0">
-                <i class="bi bi-markdown"></i> Markdown Editor
-            </span>
+            <!-- Left: Sidebar Toggle + Logo and Title -->
+            <div class="d-flex align-items-center gap-2">
+                <!-- Sidebar Toggle Button -->
+                <button id="sidebarToggleBtn" class="btn-flat btn-flat-secondary" title="Toggle Sidebar">
+                    <i class="bi bi-layout-sidebar"></i>
+                </button>
+
+                <!-- Logo and Title (Clickable) -->
+                <a href="/" class="navbar-brand mb-0" id="navbarBrand" style="cursor: pointer; text-decoration: none;">
+                    <i class="bi bi-markdown"></i> Markdown Editor
+                </a>
+            </div>
 
             <!-- Right: All Buttons -->
             <div class="ms-auto d-flex gap-2 align-items-center">
@@ -227,6 +235,7 @@
     <script src="/static/js/context-menu.js" defer></script>
     <script src="/static/js/file-upload.js" defer></script>
     <script src="/static/js/dark-mode.js" defer></script>
+    <script src="/static/js/sidebar-toggle.js" defer></script>
     <script src="/static/js/collection-selector.js" defer></script>
     <script src="/static/js/editor-drop-handler.js" defer></script>