fix(lint): resolve remaining ESLint errors (unused vars, any types, react-refresh)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/contexts/EventStreamContext.tsx

@@ -27,6 +27,7 @@ export function EventStreamProvider({
   )
 }
 
+// eslint-disable-next-line react-refresh/only-export-components
 export function useEventStreamContext() {
   return useContext(EventStreamContext)
 }