fix(v2.1.1): 修复执行问题记录中的真实 bug + 文档对齐

源码修复（5 项）:
1. search.py --time-range choices 加入 week（对齐 SearXNG API 四档）
2. fetch.py stdlib 路径处理 gzip/deflate 解压（被沙箱伪响应掩盖的真实 bug，
   无 requests 环境抓取压缩服务器会全页 U+FFFD 乱码）
3. search.py --research 模式实现跨角度合并去重，输出 merged_results 字段
   （兑现文档承诺 "Results are merged and deduplicated"）
4. search.py fetch_page 返回 error_code 字段 + AdaptiveThrottle 用
   E_RATE_LIMIT 结构化检测 429（原字符串匹配 "429" 会漏判
   "Too Many Requests"）
5. search.py _retry_with_backoff 复用 compute_backoff_delay（60s 封顶）
   + 处理 Retry-After header，与 fetch.py 保持一致

增强（3 项）:
- common.py 精确化 baidu 子域列表（pan.baidu.com/cloud.baidu.com 不再误伤）
- search.py expand_research_queries 根据主题语言切换中英文后缀
- search.py 新增 _warn_unresponsive_engines，识别实例侧引擎挂起并提示

文档/版本:
- _config.py VERSION 2.1.0 → 2.1.1
- SKILL.md 同步更新（time-range week、merged_results、error_code、baidu 精确化）
- README.md 同步更新 + 测试数量 503 → 539

测试: 539 个全部通过，含 6 个新增验证测试

tests/test_search.py

@@ -14,6 +14,7 @@ from search import (
     _merge_headers,
     _normalize_csv,
     _read_queries_file,
+    _warn_unresponsive_engines,
     deduplicate_results,
     filter_results_by_domain,
     load_config,
@@ -224,6 +225,14 @@ def test_build_params_time_range_none_excluded():
     assert "time_range" not in p
 
 
+def test_build_params_time_range_week_included():
+    """v2.1.1: 'week' is a valid SearXNG API time_range tier and must be
+    passed through to params. Previously argparse choices omitted 'week',
+    forcing users to use config-file workaround."""
+    p = _build_params("x", _Args(time_range="week"))
+    assert p["time_range"] == "week"
+
+
 def test_build_params_pageno_as_string():
     p = _build_params("x", _Args(pageno=3))
     assert p["pageno"] == "3"
@@ -252,6 +261,40 @@ def test_merge_headers_all_none():
     assert _merge_headers(None, None) == {}
 
 
+# ----- _warn_unresponsive_engines (v2.1.1) -----
+
+def test_warn_unresponsive_no_field():
+    """No unresponsive_engines field → no warning, no exception."""
+    _warn_unresponsive_engines({}, "test")
+
+
+def test_warn_unresponsive_empty_list():
+    """Empty unresponsive_engines list → no warning."""
+    _warn_unresponsive_engines({"unresponsive_engines": []}, "test")
+
+
+def test_warn_unresponsive_with_reasons():
+    """[engine, reason] format should be formatted as 'engine (reason)'."""
+    results = {"unresponsive_engines": [
+        ["brave", "Suspended: too many requests"],
+        ["duckduckgo", "CAPTCHA"],
+    ]}
+    # Should not raise; logger.warning is called internally
+    _warn_unresponsive_engines(results, "test", result_count=1)
+
+
+def test_warn_unresponsive_engine_only():
+    """[engine] single-element format should be handled."""
+    results = {"unresponsive_engines": [["brave"]]}
+    _warn_unresponsive_engines(results, "test", result_count=5)
+
+
+def test_warn_unresponsive_string_format():
+    """Plain string entries (non-list) should be handled gracefully."""
+    results = {"unresponsive_engines": ["brave", "duckduckgo"]}
+    _warn_unresponsive_engines(results, "test", result_count=0)
+
+
 # ----- deduplicate_results -----
 
 def test_dedup_removes_exact_duplicate_url():