Render blog posts on server so they are available in initial HTML
response.
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-->
## Summary by CodeRabbit
* **New Features**
* New collapsible sections for blog content
* Server-side MDX compilation for blog posts
* Improved TOC extraction producing both structured JSON and markdown
* **Refactor**
* Blog rendering converted to a server-rendered flow with unified MDX
components
* Tag handling normalized for related-post matching
* **Bug Fixes**
* Consistent image/self-closing tag normalization and corrected TOC
indentation
* Errors are now surfaced instead of being swallowed
<!-- end of auto-generated comment: release notes by coderabbit.ai -->