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/recipe-ideas/route.ts

@@ -11,6 +11,8 @@ const InputSchema = z.object({
   prompt: z.string().max(300).optional(),
 });
 
+const LANG: Record<string, string> = { en: "English", fr: "French" };
+
 const IdeasSchema = z.object({
   ideas: z.array(z.object({
     title: z.string(),
@@ -45,6 +47,9 @@ export async function POST(req: NextRequest) {
     ? `Consider the following user preferences when suggesting ideas:${bioContext}\n\n`
     : "";
 
+  const locale = (session!.user as { locale?: string }).locale ?? "en";
+  const lang = LANG[locale] ?? "English";
+
   const prompt = parsed.data.prompt?.trim()
     ? `${userContext}Generate 6 diverse recipe ideas based on: "${parsed.data.prompt}". Include a mix of difficulty levels.`
     : `${userContext}Generate 6 diverse, creative recipe ideas. Include different cuisines, difficulty levels, and meal types.`;
@@ -52,6 +57,7 @@ export async function POST(req: NextRequest) {
   const { object } = await generateObject({
     model,
     schema: IdeasSchema,
+    system: `Respond in ${lang}.`,
     prompt,
   });