feat: align browser callback runtime and export flows

Consolidate the browser task runtime around the callback path, add safer artifact opening for Zhihu exports, and cover the new service/browser flows with focused tests and supporting docs.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/compat_screen_html_export_tool_test.rs

@@ -47,4 +47,13 @@ async fn screen_html_export_tool_renders_dashboard_html_with_presentation_contra
     assert!(html.contains("问题一"));
     assert!(html.contains("344万"));
     assert!(html.contains("const defaultPayload ="));
+    assert!(html.contains("汇报摘要"));
+    assert!(html.contains("fitScreenToViewport"));
+    assert!(html.contains("dashboard-canvas"));
+    assert!(html.contains("themeSwitcher"));
+    assert!(html.contains("gov_blue_gold"));
+    assert!(html.contains("tech_cyan_blue"));
+    assert!(html.contains("industry_ink_green"));
+    assert!(html.contains("meeting_red_gold"));
+    assert!(html.contains("localStorage.setItem(\"zhihu-hotlist-theme\""));
 }