feat: Create an Options page for extension settings #41

Is your feature request related to a problem?

The extension currently has no central place for settings. Users cannot set a default translation language or customize the keyboard shortcut, forcing them to re-select their preferred language frequently and use the default shortcut.

Describe the solution you'd like

1. Create a standard Chrome Extension options page (options.html, options.js).
2. Add a link to this page from the main popup (popup.html).
3. On the options page, provide the following settings:

• A dropdown menu to select a "Default Target Language". This language should be automatically selected in the popup when the extension is opened.
• An input field to allow users to customize the keyboard shortcut for activating the code picker.

4. Use chrome.storage.sync to save these settings so they persist across the user's browsers.

Additional context

This is a standard feature for a mature browser extension. It greatly improves usability and makes the extension feel more powerful and personalized.