Add email verification functionality, including backend support, email handling, and user interface integration.

backend/build.gradle.kts

@@ -27,6 +27,7 @@ dependencies {
     implementation(project(":open_api"))
     implementation(project(":database"))
     implementation(project(":frontend"))
+    implementation(project(":discord"))
     annotationProcessor("org.projectlombok:lombok")
     implementation("com.mysql:mysql-connector-j:8.0.32")
     implementation("org.mybatis:mybatis:3.5.13")