fix: sidebar — x-data vide masquait appState() + header Notion-style + null-guards

- Sidebar avait x-data vide qui créait un scope isolé → vars (workspaceMenuOpen,
  toggleWorkspaceMenu, sidebarCollapsed) introuvables → rien ne fonctionnait
- Suppression x-data → héritage du scope appState() parent
- Header restylé Notion: .sidebar-workspace-header avec border-radius + hover bg
- Mouse hover (mouseenter/mouseleave) active wsHeaderHover → fond plus clair
- Null-guards: folderStack[-1] sécurisé, ctxMenu.node && ctxMenu.node.is_folder

app/templates/local_workspace.html

@@ -723,7 +723,7 @@
     <div class="modal-box">
       <h3><span x-text="createType==='folder'?'📁':'📄'"></span> <span x-text="createType==='folder'?'New Folder':'New File'"></span></h3>
       <p class="modal-sub">
-        In <strong>{{ workspace_name }}</strong> <span x-show="folderStack.length>1">/ <span x-text="folderStack[folderStack.length-1].name"></span></span>
+        In <strong>{{ workspace_name }}</strong> <span x-show="folderStack.length>1">/ <span x-text="(folderStack[folderStack.length-1]||{}).name||''"></span></span>
         <span x-show="parentFolder"> / <span x-text="parentFolder?.name"></span></span>
       </p>
       <input class="modal-input" x-model="newName" :placeholder="createType==='folder'?'Folder name':'File name'" @keydown.enter="doCreate" x-ref="cinp">
@@ -769,7 +769,7 @@
        @keydown.escape="ctxMenu.visible=false"
        x-transition>
     <div class="ctx-item" @click="ctxMenuOpenPage()">📄 Open</div>
-    <div class="ctx-item" x-show="ctxMenu.node.is_folder" @click="ctxMenuOpenFolder()">📂 Open folder</div>
+    <div class="ctx-item" x-show="ctxMenu.node && ctxMenu.node.is_folder" @click="ctxMenuOpenFolder()">📂 Open folder</div>
     <div class="ctx-item" @click="ctxMenuRename()">✏️ Rename</div>
     <div class="ctx-item" @click="ctxMenuDuplicate()">📋 Duplicate</div>
     <div class="ctx-sep"></div>