fix: workspace_tree 叶子判定——无子目录的目录标 is_leaf=true

原把所有目录硬编码 is_leaf:false，导致无子目录的目录(叶子)也被当成可展开的非叶子。
改为扫描子目录判断 has_subdir，is_leaf = not has_subdir。

wwwroot/api/workspace_tree.dspy

@@ -50,12 +50,21 @@ for name in entries:
     if name.startswith('.') or name == '__pycache__':
         continue
     if os.path.isdir(full):
+        # 叶子判定：目录下是否还有子目录（排除隐藏目录）。无子目录 → 叶子(不可展开)
+        has_subdir = False
+        try:
+            for sub in os.listdir(full):
+                if not sub.startswith('.') and os.path.isdir(os.path.join(full, sub)):
+                    has_subdir = True
+                    break
+        except Exception:
+            pass
         items.append({
             "id": id_prefix + name,
             "parentid": node_id,
             "label": "📁 " + name,
             "path": full,
-            "is_leaf": False
+            "is_leaf": not has_subdir
         })
 
 return items