feat(feedback): optionales E-Mail-Kontaktfeld im Formular

Nutzer können optional eine E-Mail hinterlassen; Validierung client-/serverseitig, Weitergabe in Ntfy-Benachrichtigungen.

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

server/src/services/ntfyNotify.ts

@@ -2,6 +2,7 @@ export interface FeedbackPayload {
   category: string
   message: string
   username?: string
+  contactEmail?: string
   userId: string
   logbookId?: string
   logbookTitle?: string
@@ -40,6 +41,10 @@ export async function sendFeedbackViaNtfy(payload: FeedbackPayload): Promise<voi
     `User ID: ${payload.userId}`
   ]
 
+  if (payload.contactEmail) {
+    lines.push(`Contact: ${payload.contactEmail}`)
+  }
+
   if (payload.logbookTitle || payload.logbookId) {
     lines.push(`Logbook: ${payload.logbookTitle || payload.logbookId}`)
   }