Add blog section (4 draft posts) and social post drafts for /platform funnel

Continues the content-engine plan: /platform, the homepage link, and the
small-business-infrastructure course are already live. This adds the
remaining pieces — a content/blog/ section with 4 long-form posts (kept
draft:true, so nothing goes live until reviewed) and a committed set of
~12 ready-to-copy social posts in drafts/social-posts.md.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

content/blog/_index.md

@@ -0,0 +1,4 @@
+---
+title: "Blog"
+description: "Notes on running production infrastructure for small businesses, one honest mistake at a time."
+---