feat: improve config UI (#69)

* add first concept

* completed configuration ui update

* add button for testing email configuration

* improve mobile layout

* add migration

* run formatter

* delete unnecessary modal

* remove unused comment

backend/src/config/dto/testEmail.dto.ts

@@ -0,0 +1,7 @@
+import { IsEmail, IsNotEmpty } from "class-validator";
+
+export class TestEmailDTO {
+  @IsEmail()
+  @IsNotEmpty()
+  email: string;
+}