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: [],
   });

apps/web/app/api/v1/ai/recipe-chat/route.ts

@@ -14,6 +14,8 @@ const Schema = z.object({
   question: z.string().min(1).max(500),
 });
 
+const LANG: Record<string, string> = { en: "English", fr: "French" };
+
 export async function POST(req: NextRequest) {
   const { session, response } = await requireSession();
   if (response) return response;
@@ -66,10 +68,12 @@ ${stepList || "None listed"}
   ]);
   const model = resolveModel(config);
   const bioContext = buildUserBioContext(privateBio);
+  const locale = (session!.user as { locale?: string }).locale ?? "en";
+  const lang = LANG[locale] ?? "English";
 
   const { text } = await generateText({
     model,
-    system: `You are a helpful culinary assistant. Answer questions about the following recipe concisely and accurately. If a question is not related to the recipe or cooking, politely redirect. Keep answers under 200 words.
+    system: `You are a helpful culinary assistant. Answer questions about the following recipe concisely and accurately. If a question is not related to the recipe or cooking, politely redirect. Keep answers under 200 words. Respond in ${lang}.
 
 ${recipeContext}${bioContext}`,
     prompt: parsed.data.question,

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,
   });
 

apps/web/app/api/v1/ai/substitute/route.ts

@@ -41,10 +41,13 @@ export async function POST(req: NextRequest) {
     ? { provider: parsed.data.provider, model: parsed.data.model }
     : await getDefaultProviderWithKey(session!.user.id);
 
+  const locale = (session!.user as { locale?: string }).locale ?? "en";
+
   const substitutions = await substituteIngredient(
     parsed.data.ingredient,
     context,
-    aiConfig
+    aiConfig,
+    locale
   );
 
   return NextResponse.json({ substitutions });