Add email re-validation handling with UI feedback and backend validation to prevent duplicate email verification attempts

frontend/src/app/pages/forms/appeal/appeal.component.ts

@@ -58,7 +58,7 @@ export class AppealComponent implements OnInit, OnDestroy, AfterViewInit {
   protected verifiedEmails = computed(() => this.emails()
     .filter(email => email.verified)
     .map(email => email.email.toLowerCase()));
-  protected validatedMail = signal<boolean>(false);
+  protected emailIsValid = signal<boolean>(false);
   protected dialog = inject(MatDialog);
 
   constructor(
@@ -73,10 +73,13 @@ export class AppealComponent implements OnInit, OnDestroy, AfterViewInit {
       this.emails.set(emails);
     });
     this.form.valueChanges.subscribe(() => {
-      if (this.form.getRawValue().email.toLowerCase() in this.verifiedEmails()) {
-        this.validatedMail.set(true);
+      if (this.verifiedEmails().includes(this.form.getRawValue().email.toLowerCase())) {
+        this.emailIsValid.set(true);
+      } else {
+        this.emailIsValid.set(false);
       }
     });
+
   }
 
   ngOnInit() {
@@ -225,7 +228,7 @@ export class AppealComponent implements OnInit, OnDestroy, AfterViewInit {
   }
 
   protected validateMailOrNextPage() {
-    if (this.validatedMail()) {
+    if (this.emailIsValid()) {
       this.nextPage();
       return;
     }
@@ -234,7 +237,7 @@ export class AppealComponent implements OnInit, OnDestroy, AfterViewInit {
     });
     dialogRef.afterClosed().subscribe(result => {
       if (result === true) {
-        this.validatedMail.set(true);
+        this.emailIsValid.set(true);
       }
     });
   }