fix: normalize all API responses, add error handling and reset confirmation

- Extract normalizeConfig() for consistent response normalization
- Add onError handlers to mutations with useNotify
- Add window.confirm before destructive reset action
- Add resetConfirm translation key to all locales

src/locales/en.json

@@ -1292,6 +1292,7 @@
       "emojiId": "Custom Emoji ID",
       "emojiPlaceholder": "Custom emoji ID (optional)",
       "resetAll": "Reset all styles",
+      "resetConfirm": "Reset all button styles to defaults?",
       "hidden": "Hidden",
       "customLabels": "Button labels",
       "labelPlaceholder": "Custom button text",