Bug: Extension does not work for local files loaded with the `file://` protocol.

**Steps to reproduce:**
1. Load a local file (`file://`) in Google Chrome with this extension enabled.
2. Open DevTools and navigate to the `Devtools for Tailwind CSS` panel.

**What is expected:**
The extension panel loads and allows interaction with Tailwind on the file.

**What happens:**
The message "Activating DevTools for Tailwind CSS..." is displayed and never changes. There is no observable error message printed to the console.

在 Chrome 中使用本地文件复现此问题，然后从 DevTools for Tailwind CSS 面板的激活流程开始。追踪为什么对于 file:// 页面，激活一直处于待处理状态；完成的标准是面板能够加载、支持在该文件上与 Tailwind 交互，并且不再停留在激活消息上。

由索引模型根据 Issue 内容生成。