test: skip network/live crawl by default; fix settings e2e key

- pytest_collection_modifyitems: skip @pytest.mark.network unless PROXYPOOL_RUN_NETWORK_TESTS=1
- Document opt-in in tests/README.md
- e2e: replace removed crawl_timeout with validation_timeout

Made-with: Cursor

tests/e2e/test_full_workflow.py

@@ -155,9 +155,9 @@ class TestFullWorkflow:
         assert response.status_code == 200
         original_settings = response.json()["data"]
         
-        # 2. 修改设置
+        # 2. 修改设置（爬取限时已改为各插件 crawl_timeout_seconds，不再使用全局 crawl_timeout）
         new_settings = original_settings.copy()
-        new_settings["crawl_timeout"] = 45
+        new_settings["validation_timeout"] = 8
         new_settings["auto_validate"] = not original_settings["auto_validate"]
         
         response = await client.post("/api/settings", json=new_settings)
@@ -166,7 +166,7 @@ class TestFullWorkflow:
         # 3. 验证设置已保存
         response = await client.get("/api/settings")
         saved_settings = response.json()["data"]
-        assert saved_settings["crawl_timeout"] == 45
+        assert saved_settings["validation_timeout"] == 8
         
         # 4. 恢复原始设置
         response = await client.post("/api/settings", json=original_settings)