feat: one-click shopping list from meal plan, fix ingredient merge bug

- Meal-plan page now has a direct "Add to shopping list" action for the
  currently-viewed week, instead of requiring a trip to Shopping Lists and
  manually typing the week's Monday date.
- Fixed a real under-shopping bug in shopping-lists/route.ts: when
  generating from a meal-plan week, ingredients appearing in more than one
  recipe were merged by keeping only the FIRST occurrence's quantity and
  silently dropping the rest. New mergeIngredients() (pantry-shopping-match.ts)
  groups by ingredientId (or normalized name+unit) and sums quantities
  across every recipe in the week; incompatible/unparseable units are kept
  as separate line items rather than guessed at.

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

apps/web/components/meal-plan/new-shopping-list-button.tsx

@@ -10,15 +10,27 @@ import { Dialog, DialogContent, DialogHeader, DialogTitle } from "@/components/u
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
 
-export function NewShoppingListButton() {
+export function NewShoppingListButton({
+  defaultWeekStart,
+  defaultName,
+}: {
+  /** Pre-fills and locks the source week, e.g. when generating from the currently-viewed meal-plan week. */
+  defaultWeekStart?: string;
+  defaultName?: string;
+}) {
   const t = useTranslations("mealPlan");
   const tCommon = useTranslations("common");
   const router = useRouter();
   const [open, setOpen] = useState(false);
-  const [name, setName] = useState("");
-  const [weekStart, setWeekStart] = useState("");
+  const [name, setName] = useState(defaultName ?? "");
+  const [weekStart, setWeekStart] = useState(defaultWeekStart ?? "");
   const [saving, setSaving] = useState(false);
 
+  function openDialog() {
+    if (defaultWeekStart) { setName(defaultName ?? ""); setWeekStart(defaultWeekStart); }
+    setOpen(true);
+  }
+
   async function create() {
     if (!name.trim()) return;
     setSaving(true);
@@ -44,8 +56,9 @@ export function NewShoppingListButton() {
 
   return (
     <>
-      <Button size="sm" onClick={() => setOpen(true)}>
-        <Plus className="h-4 w-4" /> {t("newList")}
+      <Button size="sm" onClick={openDialog} variant={defaultWeekStart ? "outline" : "default"}>
+        {defaultWeekStart ? <ShoppingCart className="h-4 w-4" /> : <Plus className="h-4 w-4" />}
+        {defaultWeekStart ? t("generateFromThisWeek") : t("newList")}
       </Button>
       <Dialog open={open} onOpenChange={setOpen}>
         <DialogContent className="max-w-md">
@@ -55,11 +68,16 @@ export function NewShoppingListButton() {
               <Label>{t("listNameLabel")}</Label>
               <Input value={name} onChange={(e) => setName(e.target.value)} placeholder={t("listNamePlaceholder")} />
             </div>
-            <div className="space-y-2">
-              <Label>{t("generateFromWeek")}</Label>
-              <Input type="date" value={weekStart} onChange={(e) => setWeekStart(e.target.value)} />
-              <p className="text-xs text-muted-foreground">{t("generateFromWeekHint")}</p>
-            </div>
+            {!defaultWeekStart && (
+              <div className="space-y-2">
+                <Label>{t("generateFromWeek")}</Label>
+                <Input type="date" value={weekStart} onChange={(e) => setWeekStart(e.target.value)} />
+                <p className="text-xs text-muted-foreground">{t("generateFromWeekHint")}</p>
+              </div>
+            )}
+            {defaultWeekStart && (
+              <p className="text-xs text-muted-foreground">{t("generateFromThisWeekHint")}</p>
+            )}
             <div className="flex gap-2 justify-end">
               <Button variant="outline" onClick={() => setOpen(false)}>{tCommon("cancel")}</Button>
               <Button onClick={create} disabled={!name.trim() || saving}>{saving ? t("listCreating") : t("listCreate")}</Button>