* docs: add card-based blog index page for mobile navigation
Fixes#20100 - the blog landing page showed post content directly
instead of an index, with no way to navigate between posts on mobile.
- Swizzle BlogListPage with card-based grid layout
- Featured latest post spans full width with badge
- Responsive 2-column grid with orphan handling
- Pagination, SEO metadata, accessibility (aria-label, dateTime, heading hierarchy)
- Add description frontmatter to existing blog posts
* docs: add deterministic fallback colors for unknown blog tags
* docs: rename blog heading to The LiteLLM Blog
