fix: add IP rate limiting and guard non-string email in flyer route

Adds an in-memory, IP-based fixed-window rate limit (max 3 req/hour)
to app/api/familyguard-flyer/route.ts to mitigate an email-spam/abuse
vector where any client could trigger outbound emails and DB inserts
with no limit. Also guards against a non-string `email` field in the
request body, which previously threw an uncaught TypeError (HTTP 500)
instead of the intended 400 validation response.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LhY1QhDXGWfyhrxaJvfpNt

app/api/familyguard-flyer/route.ts

@@ -4,11 +4,42 @@ import { createServiceClient } from "@/lib/supabase";
 
 const FLYER_DOWNLOAD_URL = "/downloads/MBO_FamilyGuard_Flyer_01.pdf";
 
+const RATE_LIMIT_WINDOW_MS = 60 * 60 * 1000;
+const RATE_LIMIT_MAX = 3;
+const requestLog = new Map<string, number[]>();
+
+function isRateLimited(ip: string): boolean {
+  const now = Date.now();
+  const timestamps = (requestLog.get(ip) ?? []).filter(
+    (t) => now - t < RATE_LIMIT_WINDOW_MS
+  );
+  if (timestamps.length >= RATE_LIMIT_MAX) {
+    requestLog.set(ip, timestamps);
+    return true;
+  }
+  timestamps.push(now);
+  requestLog.set(ip, timestamps);
+  return false;
+}
+
+function getClientIp(request: Request): string {
+  const forwarded = request.headers.get("x-forwarded-for");
+  if (forwarded) return forwarded.split(",")[0].trim();
+  return "unknown";
+}
+
 function isValidEmail(email: string): boolean {
   return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email);
 }
 
 export async function POST(request: Request) {
+  if (isRateLimited(getClientIp(request))) {
+    return NextResponse.json(
+      { ok: false, error: "Zu viele Anfragen. Bitte versuchen Sie es später erneut." },
+      { status: 429 }
+    );
+  }
+
   let body: { email?: string; dsgvoEinwilligung?: boolean };
   try {
     body = await request.json();
@@ -16,7 +47,7 @@ export async function POST(request: Request) {
     return NextResponse.json({ ok: false, error: "Ungültige Anfrage" }, { status: 400 });
   }
 
-  const email = body.email?.trim() ?? "";
+  const email = typeof body.email === "string" ? body.email.trim() : "";
   if (!isValidEmail(email)) {
     return NextResponse.json(
       { ok: false, error: "Bitte geben Sie eine gültige E-Mail-Adresse ein" },