feat: copy/export as Markdown wherever print exists

Added a shared ExportMarkdownButton (copy to clipboard / download .md)
next to every existing print button: recipe, shopping list,
collection, meal plan, pantry. Each surface gets a small serializer in
lib/markdown/ built from data already in scope at that page — no new
queries except pantry, where items now thread through as a prop to
PantryPageHeader instead of being fetched only for PantryManager.

Also fixes an unrelated bug hit while verifying the collection export:
RecipeCard called the client-only useTranslations() hook without
"use client", so it rendered fine everywhere it happened to run inside
an already-client tree but 500'd — "Couldn't find next-intl config
file" — when Next tried to run it as a Server Component, which only
happens on the collection detail page (its only caller). Collections
with recipes in them were completely broken.

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

apps/web/lib/markdown/shopping-list.ts

@@ -0,0 +1,27 @@
+type ShoppingListMarkdownInput = {
+  name: string;
+  items: Array<{ rawName: string; quantity: string | null; unit: string | null; aisle: string | null; checked: boolean }>;
+};
+
+export function shoppingListToMarkdown(list: ShoppingListMarkdownInput): string {
+  const lines: string[] = [`# ${list.name}`, ""];
+
+  const byAisle = new Map<string, typeof list.items>();
+  for (const item of list.items) {
+    const aisle = item.aisle ?? "Other";
+    const group = byAisle.get(aisle) ?? [];
+    group.push(item);
+    byAisle.set(aisle, group);
+  }
+
+  for (const [aisle, items] of byAisle) {
+    lines.push(`## ${aisle}`, "");
+    for (const item of items) {
+      const qty = [item.quantity, item.unit].filter(Boolean).join(" ");
+      lines.push(`- [${item.checked ? "x" : " "}] ${qty ? `${qty} ` : ""}${item.rawName}`);
+    }
+    lines.push("");
+  }
+
+  return lines.join("\n").trim() + "\n";
+}