feat: arborescence interactive avec expand/collapse, breadcrumb et navigation par dossier

- API /api/local-workspace/tree: arbre récursif complet (support optionnel ?folder=ID)
- API /api/local-workspace/breadcrumb: fil d'Ariane parent pour un dossier
- Page /local-workspace: supporte ?folder=ID pour naviguer dans un dossier
- Sidebar: expand/collapse (▶/▼) sur les dossiers, clic dossier → /local-workspace?folder=ID
- CSS: styles chevron .tree-chevron, .tree-folder-link
- Alpine.js: expandedFolders, toggleTreeFolder, navigateToFolder

app/templates/base.html

@@ -110,15 +110,30 @@
   <li class="sidebar-item ws-tree-item" 
       data-id="{{ page.db_id }}" 
       data-is-folder="{{ 'true' if page.is_folder else 'false' }}"
+      data-depth="{{ depth }}"
       draggable="true"
       @dragstart="dragStart($event, {{ page.db_id }})"
       @dragover.prevent="dragOver($event, {{ page.db_id }}, {{ 'true' if page.is_folder else 'false' }})"
       @dragleave="dragLeave($event)"
       @drop.prevent="drop($event, {{ page.db_id }})"
-      @dblclick="openWorkspacePage({{ page.db_id }})"
       style="padding-left:{{ 8 + depth * 16 }}px;">
+    {% if page.is_folder %}
+    <button class="tree-chevron" 
+            @click.stop="toggleTreeFolder({{ page.db_id }})"
+            :class="{ open: expandedFolders[{{ page.db_id }}] }"
+            title="Toggle folder">▶</button>
+    {% else %}
+    <span style="width:16px;flex-shrink:0;"></span>
+    {% endif %}
     <span class="page-icon">{{ page.icon }}</span>
+    {% if page.is_folder %}
+    <span class="page-name tree-folder-link" 
+          @click.stop="navigateToFolder({{ page.db_id }})" 
+          draggable="false"
+          title="Open folder">{{ page.name }}</span>
+    {% else %}
     <a href="/pages/{{ page.db_id }}" class="page-name" draggable="false">{{ page.name }}</a>
+    {% endif %}
     <div class="sidebar-item-actions">
       {% if page.is_folder %}
       <button class="ws-act" @click.stop="newPageInFolder({{ page.db_id }})" title="New file in folder">📄</button>
@@ -128,10 +143,14 @@
     </div>
   </li>
     {% if page.children %}
-      {{ render_workspace_tree(page.children, depth + 1) }}
+    <li x-show="expandedFolders[{{ page.db_id }}]" x-transition style="list-style:none;margin:0;padding:0;">
+      <ul style="list-style:none;margin:0;padding:0;">
+        {{ render_workspace_tree(page.children, depth + 1) }}
+      </ul>
+    </li>
     {% endif %}
   {% endfor %}
-{% endmacro %} 
+{% endmacro %}
       <div class="sidebar-section-items" x-show="sectionsOpen.workspace" x-transition>
         <ul class="sidebar-items" data-section="workspace">
           {% if workspace_pages %}
@@ -783,6 +802,16 @@
         window.location = `/pages/${pageId}`;
       },
 
+      // ── Tree expand/collapse + folder navigation ──
+      expandedFolders: {},
+      toggleTreeFolder(id) {
+        this.expandedFolders[id] = !(this.expandedFolders[id] || false);
+        this.expandedFolders = Object.assign({}, this.expandedFolders);
+      },
+      navigateToFolder(id) {
+        window.location = `/local-workspace?folder=${id}`;
+      },
+
       createEmptyPage() {
         this.showNewPageMenu = false;
         this.newPage('Private');