Fix extension loading error and update workflow branch config

[Copilot]

Extension fails to load in Chrome due to missing default_locale in manifest when _locales folder is present.

Changes

• Manifest fix: Added "default_locale": "en" to both Chrome and Edge manifest.json files. Chrome requires this field when localization files (_locales/) exist.

• Workflow update: Added main branch to test.yml pull request triggers for consistency with push-artifact.yml.

{
  "manifest_version": 3,
  "name": "Patch Reader",
  "default_locale": "en",
  ...
}

Original prompt

---

This section details on the original issue you should resolve

<issue_title>问题修复</issue_title>
<issue_description>1. 主分支是master,更新工作流
2. 加载插件时错误
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes 问题修复 #10

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.