fix(ui): hydration mismatch su /tracking e /plan (date calcolate client-side)

I React errors #418/#423/#425 segnalati dal browser nel flow di salvataggio check-in: l'HTML server-rendered divergeva dal client-rendered, causando `Text content does not match`. La submit del check-in falliva silenziosamente.

Cause:
- `weight-entry-form.tsx` calcolava `todayISO()` (basato su `new Date()`) dentro `defaultValues` di `useForm`. Il render avviene sia SSR che hydration, e fra i due il valore può differire (anche di pochi ms attraverso la mezzanotte locale, oppure per fuso orario server vs client).
- `plan-week.tsx` con `todayDayOfWeek()` aveva lo stesso problema sul pannello macros.

Fix: il valore viene calcolato server-side nel rispettivo Server Component (`tracking/page.tsx`, `plan/page.tsx`) e passato come prop al Client Component. Stabile attraverso SSR e hydration perché serializzato nell'HTML iniziale.

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

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

@@ -26,7 +26,11 @@ export default async function PlanPage({ params: { locale } }: { params: { local
 
   const [plan, dailyTarget] = await Promise.all([fetchCurrentPlan(), fetchDailyTarget()]);
 
-  return <PlanPageContent plan={plan} dailyTarget={dailyTarget} />;
+  // Calcolato server-side per evitare hydration mismatch nel pannello macros.
+  const dow = new Date().getDay();
+  const todayDayOfWeek = dow === 0 ? 6 : dow - 1;
+
+  return <PlanPageContent plan={plan} dailyTarget={dailyTarget} todayDayOfWeek={todayDayOfWeek} />;
 }
 
 const ITALIAN_DATE = new Intl.DateTimeFormat('it-IT', {
@@ -49,9 +53,11 @@ function formatWeek(weekStart: string): string {
 function PlanPageContent({
   plan,
   dailyTarget,
+  todayDayOfWeek,
 }: {
   plan: Awaited<ReturnType<typeof fetchCurrentPlan>>;
   dailyTarget: Awaited<ReturnType<typeof fetchDailyTarget>>;
+  todayDayOfWeek: number;
 }) {
   const t = useTranslations('Plan');
 
@@ -154,7 +160,7 @@ function PlanPageContent({
 
           {plan ? (
             <div className="animate-fade-up relative [animation-delay:480ms]">
-              <PlanWeek plan={plan} dailyTarget={dailyTarget} />
+              <PlanWeek plan={plan} dailyTarget={dailyTarget} todayDayOfWeek={todayDayOfWeek} />
             </div>
           ) : null}
         </main>

apps/web/src/app/[locale]/plan/plan-week.tsx

@@ -62,18 +62,16 @@ function aggregateMacros(slots: PlanSlot[]): {
 
 const FREE_MEAL_DEFAULT_KCAL = 750;
 
-// PRD §6 — il pannello macros laterale ancora oggi (lun=0…dom=6).
-function todayDayOfWeek(): number {
-  const d = new Date().getDay(); // 0 = Sunday
-  return d === 0 ? 6 : d - 1;
-}
-
 export function PlanWeek({
   plan,
   dailyTarget,
+  todayDayOfWeek,
 }: {
   plan: CurrentPlan;
   dailyTarget: DailyTarget | null;
+  /** Indice giorno corrente (lun=0…dom=6) calcolato server-side per evitare
+   * hydration mismatch fra render SSR e client. */
+  todayDayOfWeek: number;
 }) {
   const t = useTranslations('Plan');
 
@@ -83,7 +81,7 @@ export function PlanWeek({
     byDay.get(slot.dayOfWeek)!.push(slot);
   }
 
-  const today = todayDayOfWeek();
+  const today = todayDayOfWeek;
   const todaySlots = byDay.get(today) ?? [];
   const todayConsumed = aggregateMacros(todaySlots.filter((s) => s.consumed));
   const todayPlanned = aggregateMacros(todaySlots);

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

@@ -38,11 +38,16 @@ export default async function TrackingPage({ params: { locale } }: { params: { l
     fetchTodayCheckIn(),
   ]);
 
+  // Calcolato server-side per evitare hydration mismatch su WeightEntryForm.
+  const now = new Date();
+  const todayISO = `${now.getFullYear()}-${String(now.getMonth() + 1).padStart(2, '0')}-${String(now.getDate()).padStart(2, '0')}`;
+
   return (
     <TrackingPageContent
       entries={entries}
       profile={profile as ProfileLike}
       todayCheckIn={todayCheckIn}
+      todayISO={todayISO}
     />
   );
 }
@@ -51,10 +56,12 @@ function TrackingPageContent({
   entries,
   profile,
   todayCheckIn,
+  todayISO,
 }: {
   entries: Awaited<ReturnType<typeof fetchWeightEntries>>;
   profile: ProfileLike;
   todayCheckIn: Awaited<ReturnType<typeof fetchTodayCheckIn>>;
+  todayISO: string;
 }) {
   const t = useTranslations('Tracking');
   const latest = entries[0] ?? null;
@@ -135,7 +142,7 @@ function TrackingPageContent({
           <div className="relative grid gap-12 md:grid-cols-12">
             <section className="animate-fade-up [animation-delay:300ms] md:col-span-7">
               <p className="editorial-eyebrow mb-6">{t('newEntry')}</p>
-              <WeightEntryForm latest={latest} />
+              <WeightEntryForm latest={latest} todayISO={todayISO} />
             </section>
             <aside className="md:border-ink/15 animate-fade-up [animation-delay:420ms] md:col-span-5 md:border-l md:pl-10">
               <p className="editorial-eyebrow mb-6">{t('history')}</p>

apps/web/src/app/[locale]/tracking/weight-entry-form.tsx

@@ -24,12 +24,16 @@ import { Input } from '@/components/ui/input';
 
 import { saveWeightEntry, type WeightEntryRow } from './actions';
 
-function todayISO(): string {
-  const d = new Date();
-  return `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, '0')}-${String(d.getDate()).padStart(2, '0')}`;
-}
-
-export function WeightEntryForm({ latest }: { latest: WeightEntryRow | null }) {
+export function WeightEntryForm({
+  latest,
+  todayISO,
+}: {
+  latest: WeightEntryRow | null;
+  /** Data odierna in formato YYYY-MM-DD calcolata server-side. Passata
+   * come prop per evitare hydration mismatch (server e client possono
+   * differire di fuso orario o di pochi ms attraverso la mezzanotte). */
+  todayISO: string;
+}) {
   const t = useTranslations('Tracking');
   const [serverError, setServerError] = useState<string | null>(null);
   const [savedAt, setSavedAt] = useState<string | null>(null);
@@ -41,7 +45,7 @@ export function WeightEntryForm({ latest }: { latest: WeightEntryRow | null }) {
   const form = useForm<WeightEntryInput>({
     resolver: zodResolver(weightEntryInputSchema),
     defaultValues: {
-      date: todayISO(),
+      date: todayISO,
       weightKg: latest?.weightKg,
     } as unknown as WeightEntryInput,
   });
@@ -54,7 +58,7 @@ export function WeightEntryForm({ latest }: { latest: WeightEntryRow | null }) {
       return;
     }
     setSavedAt(new Date().toISOString());
-    form.reset({ date: todayISO(), weightKg: input.weightKg } as unknown as WeightEntryInput);
+    form.reset({ date: todayISO, weightKg: input.weightKg } as unknown as WeightEntryInput);
   });
 
   return (