Add Tailwind typography plugin for prose styling

The README on the home page uses prose classes which require the
typography plugin to render headers and other markdown elements.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

server.py

@@ -226,7 +226,7 @@ def sign_activity(activity: dict, username: str) -> dict:
 
 # Tailwind CSS config for L2 - dark theme to match L1
 TAILWIND_CONFIG = '''
-    <script src="https://cdn.tailwindcss.com"></script>
+    <script src="https://cdn.tailwindcss.com?plugins=typography"></script>
     <script>
         tailwind.config = {
             darkMode: 'class',