fix(walkthrough): stop the importance tag reading as a review finding

The "Critical" pill was painted in the status-error colour, so a stop marked
because it drives the change read as a severity reported against the code —
the one thing this feature never does. It is now "Key change", carries its
emphasis with weight and an outline rather than a status colour, and both tags
state their meaning in a tooltip. The panel links the guide from its header,
and the guide gained a section on what the tags mean and what they do not.

Also corrects two German strings that translated the noun "stop" as the verb.

packages/ui/src/lib/i18n/messages/uk.ts

@@ -1144,8 +1144,11 @@ export const dict: Record<I18nKey, string> = {
   "walkthrough.toc.moreFiles": "Ще файлів: {count}",
   "walkthrough.toc.uncovered": "Не описано: {count}",
   "walkthrough.toc.resize": "Змінити ширину колонки змісту",
-  "walkthrough.importance.critical": "Критично",
+  "walkthrough.importance.critical": "Ключова зміна",
+  "walkthrough.importance.criticalHint": "Цей крок веде за собою решту зміни, тож прочитайте його уважно. Це не знайдена у вашому коді проблема.",
   "walkthrough.importance.context": "Контекст",
+  "walkthrough.importance.contextHint": "Допоміжна зміна, додана, щоб решта мала сенс.",
+  "walkthrough.help.guide": "Як працюють walkthrough",
   "walkthrough.blocked.noModel.title": "Немає доступної small model",
   "walkthrough.blocked.noModel.description": "Увійдіть до провайдера моделей, щоб створити розбір.",
   "walkthrough.blocked.emptyDiff.title": "Немає що оглядати",