refactor(tree): extract _clean_join to keep entity-fields complexity at B

质量门要求新增代码复杂度不超过 B 级：将 node_entity_fields 中重复的
"清洗-去重-拼接"逻辑抽为模块级纯函数 _clean_join，主体收敛为两次
调用。radon：node_entity_fields C(13) → B(6)，_clean_join A(5)。

算法 #11（树环境语义搜索）数据访问层，行为不变（既有 4 测试未改全绿）。

app/tree/environment.py

@@ -94,6 +94,19 @@ _ENTITY_FIELDS_BY_LEVEL: dict[str, tuple[str, ...]] = {
 }
 
 
+def _clean_join(values: object) -> str:
+    """过滤非空字符串、去重（保序）、分号拼接；无有效值返回空串。
+
+    参数:
+        values: 待清洗的值集合（通常为 list[str]，容忍 None / 混入非字符串）。
+
+    返回:
+        "a; b; c" 形式的拼接串，无有效值时为空串。
+    """
+    cleaned = [v.strip() for v in (values or []) if isinstance(v, str) and v.strip()]
+    return "; ".join(dict.fromkeys(cleaned))
+
+
 def _collect_from_obj(
     obj: object,
     out: list[str],
@@ -240,23 +253,18 @@ class TreeEnvironment:
         if node is None:
             raise KeyError(f"节点不存在: {node_id}")
         level = _node_level(node)
-        out: dict[str, str] = {}
 
         entity_values: list[str] = []
         for field_name in _ENTITY_FIELDS_BY_LEVEL[level]:
-            for value in getattr(node.card, field_name) or []:
+            entity_values.extend(getattr(node.card, field_name) or [])
-                if isinstance(value, str) and value.strip():
-                    entity_values.append(value.strip())
-        if entity_values:
-            out["实体"] = "; ".join(dict.fromkeys(entity_values))
 
-        text_values = [
+        out: dict[str, str] = {}
-            v.strip()
+        entities_text = _clean_join(entity_values)
-            for v in (getattr(node.card, "visible_text", None) or [])
+        if entities_text:
-            if isinstance(v, str) and v.strip()
+            out["实体"] = entities_text
-        ]
+        visible_text = _clean_join(getattr(node.card, "visible_text", None))
-        if text_values:
+        if visible_text:
-            out["画面文字"] = "; ".join(dict.fromkeys(text_values))
+            out["画面文字"] = visible_text
         return out
 
     def search_similar(