feat(mail-service): initialize Mail-Service and integrate online nomination workflow

- Created `MailServiceApplication` with Spring Boot setup.
- Added `MailPollingService` for IMAP polling, `TurnierNr` extraction, and auto-reply functionality.
- Implemented structured email sending for online nominations via `OnlineNennungFormular`.
- Updated frontend with `Erfolgsscreen` for nomination confirmation and fallback handling.
- Added build configurations for Mail-Service and frontend nomination module.
- Documented phase-based roadmap for Online-Nennung and Mail-Service rollout.

backend/services/mail/mail-service/build.gradle.kts

@@ -0,0 +1,36 @@
+plugins {
+  alias(libs.plugins.kotlinJvm)
+  alias(libs.plugins.spring.boot)
+  alias(libs.plugins.spring.dependencyManagement)
+  alias(libs.plugins.kotlinSpring)
+}
+
+springBoot {
+  mainClass.set("at.mocode.mail.service.MailServiceApplicationKt")
+}
+
+dependencies {
+  // Interne Module
+  implementation(projects.platform.platformDependencies)
+  implementation(projects.core.coreUtils)
+  implementation(projects.core.coreDomain)
+
+  // Spring Boot Starters
+  implementation(libs.spring.boot.starter.web)
+  implementation(libs.spring.boot.starter.validation)
+  implementation(libs.spring.boot.starter.actuator)
+  implementation(libs.spring.boot.starter.mail)
+  implementation(libs.jackson.module.kotlin)
+  implementation(libs.spring.cloud.starter.consul.discovery)
+  implementation(libs.micrometer.tracing.bridge.brave)
+  implementation(libs.zipkin.reporter.brave)
+  implementation(libs.zipkin.sender.okhttp3)
+
+  // Testing
+  testImplementation(projects.platform.platformTesting)
+  testImplementation(libs.spring.boot.starter.test)
+}
+
+tasks.test {
+  useJUnitPlatform()
+}