Refactor monolithic modules and harden booking, email, and auth infrastructure.

Split oversized frontend API client, email service, and admin/booking pages into focused modules while preserving import surfaces, and add Redis-backed queues, stale booking cleanup, stronger auth, and scale deployment configs.

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

backend/src/lib/email/formatting.ts

@@ -0,0 +1,69 @@
+// Shared formatting helpers and common template variables for emails.
+
+import { db, dbGet, siteSettings } from '../../db/index.js';
+import { getCache } from '../stores/cache.js';
+
+/**
+ * Get common variables for all emails
+ */
+export function getCommonVariables(): Record<string, string> {
+  return {
+    siteName: 'Spanglish',
+    siteUrl: process.env.FRONTEND_URL || 'https://spanglish.com',
+    currentYear: new Date().getFullYear().toString(),
+    supportEmail: process.env.EMAIL_FROM || 'hello@spanglish.com',
+  };
+}
+
+/**
+ * Get the site timezone from settings (cached for performance).
+ * Cached for a short TTL via the cache abstraction (in-memory or Redis).
+ */
+export async function getSiteTimezone(): Promise<string> {
+  const cached = await getCache().get<string>('site:timezone');
+  if (cached) return cached;
+
+  const settings = await dbGet<any>(
+    (db as any).select().from(siteSettings).limit(1)
+  );
+  const timezone = settings?.timezone || 'America/Asuncion';
+  await getCache().set('site:timezone', timezone, 60);
+  return timezone;
+}
+
+/**
+ * Format date for emails using site timezone
+ */
+export function formatDate(dateStr: string, locale: string = 'en', timezone: string = 'America/Asuncion'): string {
+  const date = new Date(dateStr);
+  return date.toLocaleDateString(locale === 'es' ? 'es-ES' : 'en-US', {
+    weekday: 'long',
+    year: 'numeric',
+    month: 'long',
+    day: 'numeric',
+    timeZone: timezone,
+  });
+}
+
+/**
+ * Format time for emails using site timezone
+ */
+export function formatTime(dateStr: string, locale: string = 'en', timezone: string = 'America/Asuncion'): string {
+  const date = new Date(dateStr);
+  return date.toLocaleTimeString(locale === 'es' ? 'es-ES' : 'en-US', {
+    hour: '2-digit',
+    minute: '2-digit',
+    timeZone: timezone,
+  });
+}
+
+/**
+ * Format currency for emails. Kept distinct from lib/utils.ts formatCurrency
+ * because the email output format ("12.345 PYG" / "$10.00 USD") must not change.
+ */
+export function formatCurrency(amount: number, currency: string = 'PYG'): string {
+  if (currency === 'PYG') {
+    return `${amount.toLocaleString('es-PY')} PYG`;
+  }
+  return `$${amount.toFixed(2)} ${currency}`;
+}