## What kind of change does this PR introduce?
Add `Markdown` component
- as a ui-pattern
- docs in design-system
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Introduced a Markdown UI pattern with full documentation and a docs
sidebar entry.
* Markdown component supports composable renderers, optional lazy syntax
highlighting, and customizable element overrides.
* Added many interactive examples (full demo, headings, paragraphs,
lists, links, inline code, blockquotes, code blocks, tables, images,
horizontal rules) plus Quote and Avatar demos.
* **Documentation**
* New MDX guide detailing usage, props, and customization previews.
<!-- review_stack_entry_start -->
[](https://app.coderabbit.ai/change-stack/supabase/supabase/pull/46325?utm_source=github_walkthrough&utm_medium=github&utm_campaign=change_stack)
<!-- review_stack_entry_end -->
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
Francesco Sansalvadore