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.

Reproduce this with a local file in Chrome, then start at the DevTools for Tailwind CSS panel activation flow. Trace why activation remains pending for file:// pages; done means the panel loads, supports interaction with Tailwind on the file, and no longer remains on the activation message.

索引モデルが issue の本文から書いたものです。