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/fr.ts

@@ -968,8 +968,11 @@ export const dict = {
   'walkthrough.toc.moreFiles': 'Autres fichiers : {count}',
   'walkthrough.toc.uncovered': 'Non traité : {count}',
   'walkthrough.toc.resize': 'Redimensionner la colonne du sommaire',
-  'walkthrough.importance.critical': 'Critique',
+  'walkthrough.importance.critical': 'Changement clé',
+  'walkthrough.importance.criticalHint': "Cette étape porte l'essentiel du changement, lisez-la attentivement. Ce n'est pas un problème détecté dans votre code.",
   'walkthrough.importance.context': 'Contexte',
+  'walkthrough.importance.contextHint': 'Un changement de soutien, présent pour que le reste ait du sens.',
+  'walkthrough.help.guide': 'Comment fonctionnent les walkthroughs',
   'walkthrough.blocked.noModel.title': 'Aucun petit modèle disponible',
   'walkthrough.blocked.noModel.description': 'Connectez-vous à un fournisseur de modèles pour générer une revue.',
   'walkthrough.blocked.emptyDiff.title': 'Rien à examiner',