Replace browser confirmations with confirmation dialog

frontend/src/app/app.ts

@@ -1,6 +1,7 @@
 import { Component, computed, inject, OnInit } from '@angular/core';
 import { MatProgressSpinnerModule } from '@angular/material/progress-spinner';
 import { MatButtonModule } from '@angular/material/button';
+import { MatDialogModule } from '@angular/material/dialog';
 import { RouterOutlet } from '@angular/router';
 import { BrandMark } from './components/brand-mark';
 import { SignInPage } from './components/sign-in-page/sign-in-page';
@@ -16,6 +17,7 @@ import { SessionService } from './services/session.service';
     RouterOutlet,
     MatProgressSpinnerModule,
     MatButtonModule,
+    MatDialogModule,
   ],
   templateUrl: './app.html',
   styleUrl: './app.css',