Built-in dictionary

### Feature Request

### Problem / Opportunity

Readers on Internet Archive often encounter unfamiliar words while reading. This disrupts the reading flow and makes it harder to understand the content, especially for non-native speakers.

Adding an in-reader dictionary would improve user experience by helping readers understand content without switching tabs to google content.This could increase user engagement and reading time.

Success will be when readers can easily double-click on a word to see its definition or translation directly within the reader

### Proposal

Add a Dictionary Mode Toggle that allows users to:

- Double-click on any word to show its definition in a tooltip.
- Provide translation options if no definition is available
- Support multiple languages through auto-detection and manual selection.

Using :
- Dictionary APIs: Oxford, Merriam-Webster, Wiktionary
- Translation APIs: LibreTranslate, DeepL