Integrate Ktor HTTP clients and repositories for Veranstalter and Turnier features:

- Add `ApiRoutes` for central backend routing configuration.
- Implement `DefaultVeranstalterRepository` and `DefaultTurnierRepository` with Ktor clients.
- Add domain models (`Turnier`, `Bewerb`, `Abteilung`, `Veranstalter`) and respective repository interfaces.
- Replace fake VeranstalterRepository with real implementation.
- Update DI with `veranstalterModule` and HTTP client injection.
- Simplify TokenProvider and update HttpClient setup (timeouts, retries, logging).
- Mark roadmap tasks B-2 as partially complete.

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

@@ -15,6 +15,7 @@ kotlin {
     jvmMain.dependencies {
       implementation(projects.frontend.core.designSystem)
       implementation(projects.frontend.core.domain)
+      implementation(projects.frontend.core.network)
       implementation(projects.frontend.core.navigation)
       implementation(compose.desktop.currentOs)
       implementation(compose.foundation)
@@ -26,6 +27,8 @@ kotlin {
       implementation(libs.koin.core)
       implementation(libs.koin.compose)
       implementation(libs.koin.compose.viewmodel)
+      // Ktor client for repository implementation
+      implementation(libs.ktor.client.core)
     }
   }
 }