refactor: hand-authored pi-flow post + consolidated agents.md

- pi-flow-native-brain is now hand-authored HTML (direct SVGs + styled
  tables; no build.js passthrough needed)
- Card hardcoded in _index_template.html above {{CARDS}}
- Removed posts/pi-flow-native-brain.md (build.js no longer touches it)
- New agents.md: consolidated agent guide for the blog repo
  (blog architecture, build pipeline, adding posts, styling rules,
  writing guide, deploy instructions, skills reference)
- Removed old skills/blog.md (content migrated to agents.md)

_index_template.html

@@ -120,6 +120,13 @@
 
   <!-- BLOG LIST -->
   <div class="blog-list">
+    <!-- hand-authored HTML posts (not from build.js) -->
+    <a href="pi-flow-native-brain" class="blog-card">
+      <span class="blog-card__date">3 June 2026</span>
+      <h2 class="blog-card__title">How Pi Agents Build, Test, and Ship Game Code with Oracle-Backed Flows</h2>
+      <p class="blog-card__excerpt">When we ask Pi to build a game feature, it doesn't just write code. It compiles, runs tests, drives the live game, measures feel, fixes CI failures, and ships a green PR — all through composable oracle-backed flows.</p>
+      <span class="blog-card__read">Read &rarr;</span>
+    </a>
 {{CARDS}}
   </div>