feat: 实现AI拒答机制和语言控制优化

- 添加 RunStatus.REFUSED 状态，AI可明确表达拒答意图
- 优化 System Prompt 使用视觉强调提高AI对拒答规则的遵守
- User Prompt 添加 SCOPE CHECK 和语言约束
- Worker Rules 添加多语言版本角色扮演规则
- Runner 传递 language 参数到 worker stage
- json_finalize 添加语言约束参数
- 更新单元测试匹配新的 prompt 结构

backend/tests/unit/test_json_finalize.py

@@ -47,12 +47,41 @@ class _Model:
         return _Response(self._payload)
 
 
-def test_build_instruction_uses_output_schema_title() -> None:
+def test_build_instruction_has_schema() -> None:
     instruction = build_json_finalize_instruction(
         schema_json="{}",
         attempt=1,
     )
-    assert "[输出结构Output Schema]" in instruction
+    assert "[Output Schema]" in instruction
+
+
+def test_build_instruction_has_language_constraint_en() -> None:
+    instruction = build_json_finalize_instruction(
+        schema_json="{}",
+        attempt=1,
+        language="en-US",
+    )
+    assert "ENGLISH OUTPUT REQUIRED" in instruction
+    assert "═══════════════════════════════════════════════════════════════════════════════" in instruction
+
+
+def test_build_instruction_has_language_constraint_zh() -> None:
+    instruction = build_json_finalize_instruction(
+        schema_json="{}",
+        attempt=1,
+        language="zh-CN",
+    )
+    assert "返回 JSON。使用简体中文" in instruction
+
+
+def test_build_instruction_no_language_constraint_when_none() -> None:
+    instruction = build_json_finalize_instruction(
+        schema_json="{}",
+        attempt=1,
+        language=None,
+    )
+    assert "ENGLISH OUTPUT REQUIRED" not in instruction
+    assert "返回 JSON" not in instruction
 
 
 @pytest.mark.asyncio