feat(online-nennung): integrate online nomination workflow via REST and mail service

- Enabled web-to-backend nominations with `MailController` and REST endpoint (`/api/mail/nennung`).
- Added `NennungRemoteRepository` for frontend API integration using Ktor.
- Linked `WebMainScreen` to backend API for nomination handling and confirmation display.
- Implemented automated confirmation emails for received nominations.
- Updated `MASTER_ROADMAP` to reflect progress on Phase 13 milestones.
- Improved Nennung UI, backend persistence, and QA tracking for Neumarkt tournament.

frontend/features/nennung-feature/build.gradle.kts

@@ -10,6 +10,7 @@ plugins {
   alias(libs.plugins.kotlinMultiplatform)
   alias(libs.plugins.composeMultiplatform)
   alias(libs.plugins.composeCompiler)
+  alias(libs.plugins.kotlinSerialization)
 }
 
 group = "at.mocode.clients"
@@ -54,6 +55,8 @@ kotlin {
       implementation(libs.koin.core)
       implementation(libs.koin.compose)
       implementation(libs.koin.compose.viewmodel)
+
+      implementation(libs.bundles.ktor.client.common)
     }
 
     jvmMain.dependencies {