feat: sidebar tree dynamically refreshes after CRUD in local-workspace

- New endpoint GET /api/sidebar/workspace-tree returns sidebar tree HTML fragment
- refreshSidebarTree() in appState() fetches and replaces #sidebar-workspace-items
- Custom event 'flowdeck:sidebar-refresh' dispatched after doCreate/doRename/doDelete
- newFolderInWorkspace, deleteWorkspacePage, wsCtxAction('rename') now use
  refreshSidebarTree() instead of window.location.reload()
- Sidebar stays in sync without full page refresh

app/templates/local_workspace.html

@@ -1111,6 +1111,8 @@ window._wsInitData = (function() {
     _reloadAfterAction() {
       this._saveExpandedState();
       this._loadFolder(this.currentFolder);
+      // Notify sidebar to refresh its tree
+      document.dispatchEvent(new CustomEvent('flowdeck:sidebar-refresh'));
     },
 
     // ── Inline Rename ──
@@ -1555,6 +1557,8 @@ window._wsInitData = (function() {
           this.doFilter();
         }
         this._saveExpandedState();
+        // Notify sidebar to refresh its tree
+        document.dispatchEvent(new CustomEvent('flowdeck:sidebar-refresh'));
       }
     },