feat: Add AGB PDF attachment to booking confirmation emails

- Extend email system to support file attachments
- Add sendEmailWithAGB() function that automatically attaches AGB.pdf
- Implement AGB PDF caching for better performance
- Update booking confirmation email template with AGB notice
- Add visual highlight box in HTML email with AGB information
- Update email subject to indicate AGB attachment
- Include AGB reference in both HTML and text versions
- Ensure legal compliance by automatically sending terms with confirmations

Changes:
- email.ts: Add attachment support and AGB PDF integration
- email-templates.ts: Add AGB notice to confirmation emails
- bookings.ts: Use sendEmailWithAGB for confirmed bookings
- German localization for admin treatments component

src/server/lib/email.ts

@@ -6,11 +6,39 @@ type SendEmailParams = {
   from?: string;
   cc?: string | string[];
   bcc?: string | string[];
+  attachments?: Array<{
+    filename: string;
+    content: string; // base64 encoded
+    type?: string;
+  }>;
 };
 
+import { readFile } from "node:fs/promises";
+import { fileURLToPath } from "node:url";
+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>";
 
+// Cache for AGB PDF to avoid reading it multiple times
+let cachedAGBPDF: string | null = null;
+
+async function getAGBPDFBase64(): Promise<string | null> {
+  if (cachedAGBPDF) return cachedAGBPDF;
+  
+  try {
+    const __filename = fileURLToPath(import.meta.url);
+    const __dirname = dirname(__filename);
+    const agbPath = resolve(__dirname, "../../../AGB.pdf");
+    const buf = await readFile(agbPath);
+    cachedAGBPDF = buf.toString('base64');
+    return cachedAGBPDF;
+  } catch (error) {
+    console.warn("Could not read AGB.pdf:", error);
+    return null;
+  }
+}
+
 export async function sendEmail(params: SendEmailParams): Promise<{ success: boolean }> {
   if (!RESEND_API_KEY) {
     // In development or if not configured, skip sending but don't fail the flow
@@ -32,6 +60,7 @@ export async function sendEmail(params: SendEmailParams): Promise<{ success: boo
       html: params.html,
       cc: params.cc ? (Array.isArray(params.cc) ? params.cc : [params.cc]) : undefined,
       bcc: params.bcc ? (Array.isArray(params.bcc) ? params.bcc : [params.bcc]) : undefined,
+      attachments: params.attachments,
     }),
   });
 
@@ -43,4 +72,21 @@ export async function sendEmail(params: SendEmailParams): Promise<{ success: boo
   return { success: true };
 }
 
+export async function sendEmailWithAGB(params: SendEmailParams): Promise<{ success: boolean }> {
+  const agbBase64 = await getAGBPDFBase64();
+  
+  if (agbBase64) {
+    params.attachments = [
+      ...(params.attachments || []),
+      {
+        filename: "AGB_Stargirlnails_Kiel.pdf",
+        content: agbBase64,
+        type: "application/pdf"
+      }
+    ];
+  }
+  
+  return sendEmail(params);
+}
+