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/app/api/v1/ai/generate-from-idea/route.ts

@@ -14,6 +14,8 @@ const Schema = z.object({
   model: z.string().optional(),
 });
 
+const LANG: Record<string, string> = { en: "English", fr: "French" };
+
 export async function POST(req: NextRequest) {
   const { session, response } = await requireSession();
   if (response) return response;
@@ -30,11 +32,13 @@ export async function POST(req: NextRequest) {
   await checkAndIncrementTierLimit(session!.user.id, session!.user.tier as "free" | "pro", "aiCall");
 
   const privateBio = await getUserPrivateBio(session!.user.id);
+  const locale = (session!.user as { locale?: string }).locale ?? "en";
 
   const recipe = await generateRecipe(parsed.data.title, {
     provider: parsed.data.provider,
     model: parsed.data.model,
     userContext: privateBio ?? undefined,
+    language: LANG[locale] ?? "English",
   });
 
   const recipeId = crypto.randomUUID();
@@ -50,7 +54,7 @@ export async function POST(req: NextRequest) {
     difficulty: recipe.difficulty ?? null,
     visibility: "private",
     aiGenerated: true,
-    language: "en",
+    language: locale,
     dietaryTags: recipe.dietaryTags ?? {},
     tags: [],
   });