feat: one-click shopping list from meal plan, fix ingredient merge bug

- Meal-plan page now has a direct "Add to shopping list" action for the
  currently-viewed week, instead of requiring a trip to Shopping Lists and
  manually typing the week's Monday date.
- Fixed a real under-shopping bug in shopping-lists/route.ts: when
  generating from a meal-plan week, ingredients appearing in more than one
  recipe were merged by keeping only the FIRST occurrence's quantity and
  silently dropping the rest. New mergeIngredients() (pantry-shopping-match.ts)
  groups by ingredientId (or normalized name+unit) and sums quantities
  across every recipe in the week; incompatible/unparseable units are kept
  as separate line items rather than guessed at.

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

apps/web/messages/fr.json

@@ -687,6 +687,9 @@
     "listNamePlaceholder": "Courses de la semaine",
     "generateFromWeek": "Générer depuis une semaine du planning (facultatif)",
     "generateFromWeekHint": "Sélectionne le lundi de la semaine choisie",
+    "generateFromThisWeek": "Ajouter à la liste de courses",
+    "generateFromThisWeekHint": "Fusionne les ingrédients de toutes les recettes de cette semaine, additionne les quantités identiques et signale ce que vous avez déjà au garde-manger.",
+    "shoppingListWeekName": "Courses pour {week}",
     "listCreateFailed": "Échec de la création",
     "listCreating": "Création…",
     "listCreate": "Créer",