fix(i18n): translate remaining recipe card/detail strings, localize AI responses

Recipe cards, the recipe detail page, and meal planner still rendered raw
"{n} servings"/"{n}m cook"/"{n} srv" text and untranslated difficulty labels
outside the earlier i18n pass. Also wires the user's locale into AI features
that previously always answered in English regardless of app language:
recipe chat, ingredient substitution, recipe ideas, and generate-from-idea.
The recipe-language picker in the AI generate dialog now defaults to the
user's locale instead of always defaulting to English.

apps/web/components/meal-plan/meal-planner.tsx

@@ -273,7 +273,7 @@ export function MealPlanner({
                       {entry?.recipe ? (
                         <div className="group relative rounded-lg bg-primary/10 border border-primary/20 p-2 text-xs min-h-[52px]">
                           <div className="font-medium line-clamp-2 pr-4">{entry.recipe.title}</div>
-                          <div className="text-muted-foreground mt-0.5">{entry.servings} srv</div>
+                          <div className="text-muted-foreground mt-0.5">{t("servingsAbbrev", { count: entry.servings })}</div>
                           <button
                             onClick={() => removeEntry(entry)}
                             className="absolute top-1 right-1 opacity-0 group-hover:opacity-100 transition-opacity text-muted-foreground hover:text-destructive"