🇪🇸 Add Spanish translation for user guide and popup

[projekta2]

## Description The extension is bilingual (EN/ES) but the in-extension documentation (docs.html`) is currently only in English. We need to add a Spanish version.

Tasks

• Translate docs.html content to Spanish
• Add language switcher in the docs page (if not present)
• Ensure the same layout and styling

Expected outcome

Users who set Spanish language should see the guide in Spanish.

Good first issue – I can help with guidance if needed.`

[projekta2]

This is a good first issue for someone who speaks Spanish and wants to contribute to open source.

The extension is already bilingual (EN/ES) in the UI, but the in‑extension documentation (docs.html) is currently only in English.

What needs to be done:

• Translate the content of docs.html (the user guide) into Spanish
• Keep the same HTML structure and styling
• Ensure the language switcher (EN/ES) also changes the docs page

I can provide the English source file and explain where the language switcher logic lives. If you're interested, leave a comment and I'll assign this issue to you.

I'll also be available to answer questions throughout the process.