feat(markdown): enable Satteri authoring features

www/astro.config.mjs

@@ -1,5 +1,6 @@
 import { defineConfig } from 'astro/config';
 import mdx from '@astrojs/mdx';
+import { satteri } from '@astrojs/markdown-satteri';
 
 export default defineConfig({
   site: 'https://www.azinstitute4autism.com',
@@ -7,6 +8,12 @@ export default defineConfig({
   compressHTML: true,
   integrations: [mdx()],
   markdown: {
+    processor: satteri({
+      features: {
+        headingAttributes: true,
+        directive: true
+      }
+    }),
     shikiConfig: { theme: 'github-light' }
   }
 });