Replace 90+ JavaScript style assignments with semantic CSS classes in
settings panel. Improves maintainability and follows Obsidian plugin
guidelines requiring styles in CSS files rather than JavaScript.
Changes:
- Add semantic CSS classes to styles.css for auth sections, tabs,
config display, labels, and helper text
- Replace all .style.* assignments in settings.ts with CSS classes
- Use conditional class application for dynamic tab active state
- Preserve all existing functionality and visual appearance
Addresses ObsidianReviewBot requirement for PR #8298