feat(web): weekly meal plan UI with regenerate + per-slot swap

apps/api:
- New PATCH /me/meal-plans/slots/:slotId — accepts { recipeId } and validates
  ownership + that the new recipe is one of the slot's existing alternatives
  (or already selected). Returns the updated slot with the new selected recipe.

apps/web — /plan route:
- Server component runs the same auth+disclaimer+profile guard chain as
  /profile, then redirects to /profile if no profile exists yet (you can't
  generate a plan without macros)
- actions.ts exposes three server actions: fetchCurrentPlan, regeneratePlan
  and swapSlotRecipe; all proxy to api with the user's session cookie and
  revalidatePath('/plan') after writes
- plan-week.tsx renders day-by-day sections (Lun→Dom) with a 4-card meal
  row (1/2/4 columns at sm/lg breakpoints), recipe name + kcal, daily kcal
  totals, expandable list of alternatives with one-click "Scegli"
- "Genera piano" CTA when there's no plan yet, "Rigenera" when there is one
- Italian copy under Plan.* with day, meal and kcal-total interpolations
- Home gains a "Vedi il piano settimanale" CTA next to "Completa profilo"

Verified end-to-end in Chrome:
- generate plan → 7 sections (Lun-Dom), each with 4 meal cards and per-day
  kcal sum (e.g. Lunedì 1510 kcal = 360+540+150+460)
- recently-consumed penalty visible: Mon/Tue/Wed have different breakfasts
- swap: clicked "Vedi 3 alternative" on Mon Colazione → "Scegli" on
  "Uova strapazzate" → card refreshed to that recipe and 410 kcal

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/app/[locale]/plan/page.tsx

@@ -0,0 +1,53 @@
+import { prisma } from '@ketopath/db';
+import { redirect } from 'next/navigation';
+import { useTranslations } from 'next-intl';
+import { setRequestLocale } from 'next-intl/server';
+
+import { Button } from '@/components/ui/button';
+import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card';
+import { getServerSession } from '@/lib/auth';
+
+import { fetchCurrentPlan, regeneratePlan } from './actions';
+import { PlanWeek } from './plan-week';
+
+export default async function PlanPage({ params: { locale } }: { params: { locale: string } }) {
+  setRequestLocale(locale);
+  const session = await getServerSession();
+  if (!session?.user) redirect('/sign-in');
+
+  const user = await prisma.user.findUnique({
+    where: { id: session.user.id },
+    select: { disclaimerAcceptedAt: true, profile: { select: { id: true } } },
+  });
+  if (!user?.disclaimerAcceptedAt) redirect('/welcome');
+  if (!user.profile) redirect('/profile');
+
+  const plan = await fetchCurrentPlan();
+
+  return <PlanPageContent plan={plan} />;
+}
+
+function PlanPageContent({ plan }: { plan: Awaited<ReturnType<typeof fetchCurrentPlan>> }) {
+  const t = useTranslations('Plan');
+
+  return (
+    <main className="mx-auto min-h-screen max-w-5xl px-4 py-10 sm:px-6">
+      <Card>
+        <CardHeader className="flex flex-row items-start justify-between gap-4">
+          <div>
+            <CardTitle>{t('title')}</CardTitle>
+            <CardDescription>
+              {plan ? t('weekOf', { date: plan.weekStart }) : t('noPlan')}
+            </CardDescription>
+          </div>
+          <form action={regeneratePlan}>
+            <Button type="submit" variant={plan ? 'outline' : 'default'} size="sm">
+              {plan ? t('regenerate') : t('generate')}
+            </Button>
+          </form>
+        </CardHeader>
+        <CardContent>{plan ? <PlanWeek plan={plan} /> : null}</CardContent>
+      </Card>
+    </main>
+  );
+}