fix(hands): 集成 SearXNG 元搜索引擎 — 替换不可用的 DuckDuckGo Instant Answer API

- ResearcherHand 新增 search_searxng() 方法，调用 SearXNG JSON API 聚合 70+ 搜索引擎
- SearchEngine 枚举增加 SearXNG 变体，路由逻辑按配置分发搜索后端
- Auto 模式: SearXNG 优先 → DuckDuckGo fallback
- config.toml [tools.web.search] 新增 searxng_url/searxng_timeout 配置
- docker-compose.yml 新增 SearXNG 服务容器 (searxng-config/settings.yml)
- 新增 6 个 SearXNG 相关单元测试 (响应解析/URL构造/分数归一化/配置加载)
- 验证: 124 tests PASS, workspace 0 warnings

docker-compose.yml

@@ -69,9 +69,28 @@ services:
     networks:
       - zclaw-saas
 
+  # ---- SearXNG Meta Search ----
+  searxng:
+    image: searxng/searxng:latest
+    container_name: zclaw-searxng
+    restart: unless-stopped
+
+    volumes:
+      - ./searxng-config/:/etc/searxng/:Z
+      - searxng-data:/var/cache/searxng/
+
+    networks:
+      - zclaw-saas
+
+    # 端口仅本地访问，不对外暴露
+    ports:
+      - "127.0.0.1:8888:8888"
+
 volumes:
   postgres_data:
     driver: local
+  searxng-data:
+    driver: local
 
 networks:
   zclaw-saas: