Aggiunge newsletter custom con D1, double opt-in e invio campagne.

Attiva il form footer, API subscribe/confirm/unsubscribe e endpoint admin protetti, riusando Resend per le email.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/data/home/footer.ts

@@ -45,9 +45,9 @@ const footerByLocale = {
       description: 'Aggiornamenti su prodotti e roadmap.',
       placeholder: 'La tua email',
       buttonLabel: 'Iscriviti',
-      actionUrl: '',
+      actionUrl: '/api/newsletter/subscribe',
       fieldName: 'email',
-      successRedirect: '',
+      successRedirect: '/newsletter/grazie',
       notifySubject: 'Nuova iscrizione newsletter — NexStudio',
     },
     labels: {
@@ -101,9 +101,9 @@ const footerByLocale = {
       description: 'Updates on products and roadmap.',
       placeholder: 'Your email',
       buttonLabel: 'Subscribe',
-      actionUrl: '',
+      actionUrl: '/api/newsletter/subscribe',
       fieldName: 'email',
-      successRedirect: '',
+      successRedirect: '/en/newsletter/grazie',
       notifySubject: 'New newsletter signup — NexStudio',
     },
     labels: {
@@ -157,9 +157,9 @@ const footerByLocale = {
       description: 'อัปเดตเกี่ยวกับผลิตภัณฑ์และโรดแมป',
       placeholder: 'อีเมลของคุณ',
       buttonLabel: 'สมัครรับข่าวสาร',
-      actionUrl: '',
+      actionUrl: '/api/newsletter/subscribe',
       fieldName: 'email',
-      successRedirect: '',
+      successRedirect: '/th/newsletter/grazie',
       notifySubject: 'มีผู้สมัครจดหมายข่าวใหม่ — NexStudio',
     },
     labels: {