chore: replace em dashes with hyphens, add no-em-dash rule to CLAUDE.md

nginx.conf

@@ -11,7 +11,7 @@ server {
         return 302 /docs/;
     }
 
-    # Hashed assets are immutable — the filename changes when the content does.
+    # Hashed assets are immutable - the filename changes when the content does.
     location /docs/assets/ {
         expires 1y;
         add_header Cache-Control "public, immutable";