feat: ICS-Kalendereinträge, Rate-Limiting und erweiterte E-Mail-Validierung

- ICS-Dateianhänge in Bestätigungsmails mit Europe/Berlin Zeitzone
- Rate-Limiting: IP-basiert (5/10min) und E-Mail-basiert (3/1h)
- Mehrschichtige E-Mail-Validierung mit Rapid Email Validator API
  - Disposable Email Detection (blockiert Wegwerf-Adressen)
  - MX Record Verification
  - Domain Verification
  - Typo-Erkennung mit Vorschlägen
- Zod-Schema-Validierung für Name, E-Mail und Telefonnummer
- Dokumentation für Rate-Limiting und E-Mail-Validierung
- README mit neuen Features aktualisiert
- Backlog aktualisiert

src/server/lib/email.ts

@@ -20,6 +20,90 @@ import { dirname, resolve } from "node:path";
 const RESEND_API_KEY = process.env.RESEND_API_KEY;
 const DEFAULT_FROM = process.env.EMAIL_FROM || "Stargirlnails <no-reply@stargirlnails.de>";
 
+// Helper function to format dates for ICS files (YYYYMMDDTHHMMSS)
+function formatDateForICS(date: string, time: string): string {
+  // date is in YYYY-MM-DD format, time is in HH:MM format
+  const [year, month, day] = date.split('-');
+  const [hours, minutes] = time.split(':');
+  return `${year}${month}${day}T${hours}${minutes}00`;
+}
+
+// Helper function to create ICS (iCalendar) file content
+function createICSFile(params: {
+  date: string; // YYYY-MM-DD
+  time: string; // HH:MM
+  durationMinutes: number;
+  customerName: string;
+  treatmentName: string;
+}): string {
+  const { date, time, durationMinutes, customerName, treatmentName } = params;
+  
+  // Calculate start and end times in Europe/Berlin timezone
+  const dtStart = formatDateForICS(date, time);
+  
+  // Calculate end time
+  const [hours, minutes] = time.split(':').map(Number);
+  const startDate = new Date(`${date}T${time}:00`);
+  const endDate = new Date(startDate.getTime() + durationMinutes * 60000);
+  const endHours = String(endDate.getHours()).padStart(2, '0');
+  const endMinutes = String(endDate.getMinutes()).padStart(2, '0');
+  const dtEnd = formatDateForICS(date, `${endHours}:${endMinutes}`);
+  
+  // Create unique ID for this event
+  const uid = `booking-${Date.now()}-${Math.random().toString(36).substr(2, 9)}@stargirlnails.de`;
+  
+  // Current timestamp for DTSTAMP
+  const now = new Date();
+  const dtstamp = now.toISOString().replace(/[-:]/g, '').split('.')[0] + 'Z';
+  
+  // ICS content
+  const icsContent = [
+    'BEGIN:VCALENDAR',
+    'VERSION:2.0',
+    'PRODID:-//Stargirlnails Kiel//Booking System//DE',
+    'CALSCALE:GREGORIAN',
+    'METHOD:REQUEST',
+    'BEGIN:VEVENT',
+    `UID:${uid}`,
+    `DTSTAMP:${dtstamp}`,
+    `DTSTART;TZID=Europe/Berlin:${dtStart}`,
+    `DTEND;TZID=Europe/Berlin:${dtEnd}`,
+    `SUMMARY:${treatmentName} - Stargirlnails Kiel`,
+    `DESCRIPTION:Termin für ${treatmentName} bei Stargirlnails Kiel`,
+    'LOCATION:Stargirlnails Kiel',
+    `ORGANIZER;CN=Stargirlnails Kiel:mailto:${process.env.EMAIL_FROM?.match(/<(.+)>/)?.[1] || 'no-reply@stargirlnails.de'}`,
+    `ATTENDEE;CN=${customerName};RSVP=TRUE:mailto:${customerName}`,
+    'STATUS:CONFIRMED',
+    'SEQUENCE:0',
+    'BEGIN:VALARM',
+    'TRIGGER:-PT24H',
+    'ACTION:DISPLAY',
+    'DESCRIPTION:Erinnerung: Termin morgen bei Stargirlnails Kiel',
+    'END:VALARM',
+    'END:VEVENT',
+    'BEGIN:VTIMEZONE',
+    'TZID:Europe/Berlin',
+    'BEGIN:DAYLIGHT',
+    'TZOFFSETFROM:+0100',
+    'TZOFFSETTO:+0200',
+    'TZNAME:CEST',
+    'DTSTART:19700329T020000',
+    'RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU',
+    'END:DAYLIGHT',
+    'BEGIN:STANDARD',
+    'TZOFFSETFROM:+0200',
+    'TZOFFSETTO:+0100',
+    'TZNAME:CET',
+    'DTSTART:19701025T030000',
+    'RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU',
+    'END:STANDARD',
+    'END:VTIMEZONE',
+    'END:VCALENDAR'
+  ].join('\r\n');
+  
+  return icsContent;
+}
+
 // Cache for AGB PDF to avoid reading it multiple times
 let cachedAGBPDF: string | null = null;
 
@@ -89,6 +173,42 @@ export async function sendEmailWithAGB(params: SendEmailParams): Promise<{ succe
   return sendEmail(params);
 }
 
+export async function sendEmailWithAGBAndCalendar(
+  params: SendEmailParams,
+  calendarParams: {
+    date: string;
+    time: string;
+    durationMinutes: number;
+    customerName: string;
+    treatmentName: string;
+  }
+): Promise<{ success: boolean }> {
+  const agbBase64 = await getAGBPDFBase64();
+  
+  // Create ICS file content
+  const icsContent = createICSFile(calendarParams);
+  const icsBase64 = Buffer.from(icsContent, 'utf-8').toString('base64');
+  
+  // Attach both AGB and ICS file
+  params.attachments = [...(params.attachments || [])];
+  
+  if (agbBase64) {
+    params.attachments.push({
+      filename: "AGB_Stargirlnails_Kiel.pdf",
+      content: agbBase64,
+      type: "application/pdf"
+    });
+  }
+  
+  params.attachments.push({
+    filename: "Termin_Stargirlnails.ics",
+    content: icsBase64,
+    type: "text/calendar"
+  });
+  
+  return sendEmail(params);
+}
+
 export async function sendEmailWithInspirationPhoto(
   params: SendEmailParams, 
   photoData: string,