feat: raw HTML passthrough, details styling, accent headings

- Allow raw HTML in markdown (html.WithUnsafe) for <details> blocks
- Style <details>/<summary> with purple gradient, custom markers
- h2/h3 headings now accent purple to distinguish from body text
- Second blog post: "Transformers and Neural Networks"

👾 Generated with [Letta Code](https://letta.com)

Co-Authored-By: Letta Code <noreply@letta.com>

blog/store.go

@@ -16,7 +16,7 @@ import (
 
 var md = goldmark.New(
 	goldmark.WithExtensions(extension.GFM),
-	goldmark.WithRendererOptions(html.WithHardWraps()),
+	goldmark.WithRendererOptions(html.WithHardWraps(), html.WithUnsafe()),
 )
 
 type Post struct {