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/src/main/resources/application.yaml

@@ -0,0 +1,32 @@
+spring:
+  application:
+    name: mail-service
+  mail:
+    host: ${MAIL_HOST:imap.world4you.com}
+    port: ${MAIL_PORT:993}
+    username: ${MAIL_USERNAME:online-nennen@mo-code.at}
+    password: ${MAIL_PASSWORD:}
+    properties:
+      mail:
+        store:
+          protocol: imaps
+        imaps:
+          host: ${MAIL_HOST:imap.world4you.com}
+          port: ${MAIL_PORT:993}
+          ssl:
+            enable: true
+        smtp:
+          auth: true
+          starttls:
+            enable: true
+    host-smtp: ${SMTP_HOST:smtp.world4you.com}
+    port-smtp: ${SMTP_PORT:587}
+
+server:
+  port: 8085
+
+management:
+  endpoints:
+    web:
+      exposure:
+        include: "health,info,prometheus"