fix: recipe version diff readability + i18n, tooltip on markdown export

- Version compare used positional (index-by-index) list alignment —
  inserting one ingredient in the middle shifted every subsequent line
  out of alignment, making the whole rest of the list look changed.
  Switch to diffArrays (LCS-based) so insertions/deletions are
  detected properly; adjacent removed+added chunks still get paired
  for word-level diffing so a single edited item doesn't render as a
  full delete+insert.
- Translated "Title"/"Description"/"Ingredients"/"Steps" diff section
  headers, "Version History" sheet title, compare/restore buttons,
  loading/empty states, and the version-detail ingredient/step count
  summary (with proper plural forms).
- formatDate() in version history was hardcoded to "en-US" regardless
  of the app's locale — now uses the session locale.
- ExportMarkdownButton had no hover tooltip (bare title attribute) —
  wrap it in the same Tooltip pattern every other icon button in the
  toolbar uses.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/messages/fr.json

@@ -113,6 +113,19 @@
     "urlImportFetchFailed": "Échec de l'importation de la recette",
     "urlImportSaveFailed": "Échec de l'enregistrement de la recette importée",
     "urlImportSuccess": "Recette importée ! Vérifiez-la avant de la publier.",
+    "diffTitleLabel": "Titre",
+    "diffDescriptionLabel": "Description",
+    "diffIngredientsLabel": "Ingrédients",
+    "diffStepsLabel": "Étapes",
+    "versionHistoryTitle": "Historique des versions",
+    "versionsLoading": "Chargement des versions...",
+    "versionsEmpty": "Aucune version pour l'instant. Les versions sont enregistrées automatiquement lorsque vous modifiez cette recette.",
+    "versionCompare": "Comparer",
+    "versionCompareWith": "Comparer v{version} avec la version actuelle",
+    "versionRestore": "Restaurer",
+    "versionRestored": "Recette restaurée à la version {version}",
+    "versionDetailLoading": "Chargement...",
+    "versionDetailSummary": "{ingredients, plural, one {1 ingrédient} other {{ingredients} ingrédients}}, {steps, plural, one {1 étape} other {{steps} étapes}}",
     "analyzingPhoto": "Analyse de la photo…",
     "pairMealTooltip": "Accorder un plat",
     "historyTooltip": "Historique",