feat: save user theme preference

app/user/validators/update_theme_validator.ts

@@ -1,7 +1,8 @@
+import { THEMES } from '#user/constants/theme';
 import vine from '@vinejs/vine';
 
 export const updateThemeValidator = vine.compile(
 	vine.object({
-		preferDarkTheme: vine.boolean(),
+		theme: vine.enum(THEMES),
 	})
 );