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_wayback_shared.py

@@ -113,12 +113,21 @@ class TestIsHardBlockedDomain:
         assert is_hard_blocked_domain("https://github.com/python/cpython") is False
 
     def test_baidu_search_not_blocked(self):
-        """baidu.com search page is NOT in the hard-blocked list — only subdomains
-        like baike.baidu.com, zhidao.baidu.com are."""
-        # Actually, baidu.com is in _SUBDOMAIN_BLOCKED, so www.baidu.com matches.
-        # This is intentional — Baidu's main search also has strong anti-bot.
+        """www.baidu.com search page is in the hard-blocked list.
+        v2.1.0: moved from _SUBDOMAIN_BLOCKED (baidu.com) to HARD_BLOCKED_DOMAINS
+        (www.baidu.com) to avoid blocking pan.baidu.com / cloud.baidu.com."""
         assert is_hard_blocked_domain("https://www.baidu.com/s?wd=test") is True
 
+    def test_baidu_pan_not_blocked(self):
+        """pan.baidu.com (百度网盘) should NOT be blocked after v2.1.0 fix.
+        Previously matched by _SUBDOMAIN_BLOCKED 'baidu.com' — now only
+        www/baike/zhidao/tieba/wenku are in the precise list."""
+        assert is_hard_blocked_domain("https://pan.baidu.com/s/abc123") is False
+
+    def test_baidu_cloud_not_blocked(self):
+        """cloud.baidu.com (百度智能云) should NOT be blocked after v2.1.0 fix."""
+        assert is_hard_blocked_domain("https://cloud.baidu.com/product/abc") is False
+
     def test_empty_url(self):
         assert is_hard_blocked_domain("") is False