Fix rubocop linting issues in API chat endpoints

- Fix trailing whitespace
- Add missing final newlines
- Fix array bracket spacing
- Auto-corrected all layout issues

🤖 Generated with [Claude Code](https://claude.ai/code)

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

app/views/api/v1/chats/index.json.jbuilder

@@ -15,4 +15,4 @@ json.pagination do
   json.per_page @pagy.vars[:items]
   json.total_count @pagy.count
   json.total_pages @pagy.pages
-end
+end