feat: custom lang highlight, images dir, width bump, first post

- Wire up Ergon and ArchASM custom highlight.js languages
- Serve /content/images/ for post image embeds
- Blog width 820px -> 1040px to match landing page
- First real blog post: "Why make a blog?"

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

docker-compose.yml

@@ -5,4 +5,5 @@ services:
       - "8993:8000"
     volumes:
       - ./content/posts:/app/content/posts
+      - ./content/images:/app/content/images
     restart: unless-stopped