fix: address code review comments

- Use DEFAULT_THEME constant for theme reset
- Type user selector properly
- Include LOCALE_CONFIG in preferences cleanup
- Add newline to migration file

src/lib/client.ts

@@ -67,5 +67,6 @@ export function setClientPreferences(preferences: {
 export function removeClientPreferences() {
   removeItem(DATE_RANGE_CONFIG);
   removeItem(TIMEZONE_CONFIG);
+  removeItem(LOCALE_CONFIG);
   removeItem(THEME_CONFIG);
 }