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/plan-week.tsx

@@ -0,0 +1,117 @@
+'use client';
+
+import { useTranslations } from 'next-intl';
+import { useState, useTransition } from 'react';
+
+import { Button } from '@/components/ui/button';
+
+import { swapSlotRecipe, type CurrentPlan, type PlanSlot } from './actions';
+
+const MEAL_ORDER: PlanSlot['meal'][] = ['COLAZIONE', 'PRANZO', 'SPUNTINO', 'CENA'];
+const DAY_KEYS = [
+  'monday',
+  'tuesday',
+  'wednesday',
+  'thursday',
+  'friday',
+  'saturday',
+  'sunday',
+] as const;
+
+export function PlanWeek({ plan }: { plan: CurrentPlan }) {
+  const t = useTranslations('Plan');
+
+  // Group slots by day for quick lookup.
+  const byDay = new Map<number, PlanSlot[]>();
+  for (const slot of plan.slots) {
+    if (!byDay.has(slot.dayOfWeek)) byDay.set(slot.dayOfWeek, []);
+    byDay.get(slot.dayOfWeek)!.push(slot);
+  }
+
+  return (
+    <div className="space-y-6">
+      {DAY_KEYS.map((dayKey, idx) => {
+        const slots = (byDay.get(idx) ?? []).sort(
+          (a, b) => MEAL_ORDER.indexOf(a.meal) - MEAL_ORDER.indexOf(b.meal),
+        );
+        const dayKcal = slots.reduce((sum, s) => sum + (s.selected?.kcal ?? 0), 0);
+        return (
+          <section key={dayKey} aria-labelledby={`day-${dayKey}`}>
+            <header className="mb-2 flex items-baseline justify-between">
+              <h2 id={`day-${dayKey}`} className="text-lg font-semibold">
+                {t(`days.${dayKey}`)}
+              </h2>
+              <span className="text-muted-foreground text-xs">
+                {t('dayTotal', { kcal: Math.round(dayKcal) })}
+              </span>
+            </header>
+            <div className="grid grid-cols-1 gap-3 sm:grid-cols-2 lg:grid-cols-4">
+              {slots.map((slot) => (
+                <SlotCard key={slot.id} slot={slot} />
+              ))}
+            </div>
+          </section>
+        );
+      })}
+    </div>
+  );
+}
+
+function SlotCard({ slot }: { slot: PlanSlot }) {
+  const t = useTranslations('Plan');
+  const [open, setOpen] = useState(false);
+  const [pending, startTransition] = useTransition();
+
+  function swap(recipeId: string) {
+    startTransition(async () => {
+      await swapSlotRecipe(slot.id, recipeId);
+      setOpen(false);
+    });
+  }
+
+  return (
+    <article className="border-border bg-card flex flex-col rounded-md border p-3">
+      <p className="text-muted-foreground text-xs uppercase tracking-wider">
+        {t(`meals.${slot.meal}`)}
+      </p>
+      <p className="mt-1 text-sm font-medium leading-tight">
+        {slot.selected?.name ?? t('noRecipe')}
+      </p>
+      {slot.selected ? (
+        <p className="text-muted-foreground mt-1 text-xs">{Math.round(slot.selected.kcal)} kcal</p>
+      ) : null}
+      {slot.alternatives.length > 0 ? (
+        <div className="mt-2">
+          <button
+            type="button"
+            onClick={() => setOpen((v) => !v)}
+            className="text-primary text-xs hover:underline"
+          >
+            {open ? t('hideAlternatives') : t('showAlternatives', { n: slot.alternatives.length })}
+          </button>
+          {open ? (
+            <ul className="mt-2 space-y-1">
+              {slot.alternatives.map((alt) => (
+                <li key={alt.id} className="flex items-center justify-between gap-2">
+                  <span className="text-xs">
+                    {alt.name}{' '}
+                    <span className="text-muted-foreground">({Math.round(alt.kcal)} kcal)</span>
+                  </span>
+                  <Button
+                    type="button"
+                    size="sm"
+                    variant="ghost"
+                    disabled={pending}
+                    onClick={() => swap(alt.id)}
+                  >
+                    {t('swap')}
+                  </Button>
+                </li>
+              ))}
+            </ul>
+          ) : null}
+        </div>
+      ) : null}
+    </article>
+  );
+}