Add debug mode with hover tooltips showing element class names

[paulpv]

To help understand what content is being spoken and troubleshoot issues, add a debug mode that shows element class names on hover.

Features:

• Add "Debug Mode" toggle in popup UI (checkbox or toggle switch)
• When enabled, add hover tooltips to all div elements under TaskChat-module__stickableContainer--*
• Tooltip shows the element's class name(s)
• Focus on key containers: Session-module__detailsContainer--*, Tool-module__detailsContainer--*, MarkdownRenderer-module__container--*, etc.

Implementation:

• Store debug mode state in chrome.storage
• Inject CSS and data attributes to show tooltips
• Use title attribute or custom tooltip div

UI Mockup:

[✓] Debug Mode