chore(format): endOfLine auto so format:check is stable under git autocrlf

Prettier's LF default fought git's CRLF checkout on Windows, failing
format:check on every file with no real diff. 'auto' keeps whatever the
checkout uses; content style is unchanged.

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

.prettierrc

@@ -2,5 +2,6 @@
   "semi": false,
   "singleQuote": true,
   "printWidth": 100,
-  "trailingComma": "none"
+  "trailingComma": "none",
+  "endOfLine": "auto"
 }