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>

skills-lock.json

@@ -0,0 +1,10 @@
+{
+  "version": 1,
+  "skills": {
+    "ui-ux-pro-max": {
+      "source": "nextlevelbuilder/ui-ux-pro-max-skill",
+      "sourceType": "github",
+      "computedHash": "6337038fe1fe6bbe1b9f252ab678ee575859190bab6f0f246f4061824eb40875"
+    }
+  }
+}