Introduce Ktor-based HTTP server for Masterdata context, implement upsert logic for Altersklasse, Bundesland, and Land repositories, enhance IdempotencyPlugin, and add integration tests.

backend/services/masterdata/masterdata-common/src/main/kotlin/at/mocode/masterdata/application/usecase/CreateAltersklasseUseCase.kt

@@ -121,8 +121,8 @@ class CreateAltersklasseUseCase(
             updatedAt = now
         )
 
-        // Save to repository
-        val savedAltersklasse = altersklasseRepository.save(altersklasse)
+        // Upsert anhand des natürlichen Schlüssels (altersklasseCode)
+        val savedAltersklasse = altersklasseRepository.upsertByCode(altersklasse)
         return CreateAltersklasseResponse(
             altersklasse = savedAltersklasse,
             success = true

backend/services/masterdata/masterdata-common/src/main/kotlin/at/mocode/masterdata/application/usecase/CreateBundeslandUseCase.kt

@@ -117,8 +117,8 @@ class CreateBundeslandUseCase(
             updatedAt = now
         )
 
-        // Save to repository
-        val savedBundesland = bundeslandRepository.save(bundesland)
+        // Upsert anhand des natürlichen Schlüssels (landId + kuerzel)
+        val savedBundesland = bundeslandRepository.upsertByLandIdAndKuerzel(bundesland)
         return CreateBundeslandResponse(
             bundesland = savedBundesland,
             success = true

backend/services/masterdata/masterdata-common/src/main/kotlin/at/mocode/masterdata/application/usecase/CreateCountryUseCase.kt

@@ -123,8 +123,8 @@ class CreateCountryUseCase(
             updatedAt = now
         )
 
-        // Save to repository
-        val savedCountry = landRepository.save(country)
+        // Upsert anhand des natürlichen Schlüssels (ISO Alpha-3)
+        val savedCountry = landRepository.upsertByIsoAlpha3(country)
         return CreateCountryResponse(
             country = savedCountry,
             success = true

backend/services/masterdata/masterdata-common/src/main/kotlin/at/mocode/masterdata/application/usecase/CreatePlatzUseCase.kt

@@ -115,8 +115,8 @@ class CreatePlatzUseCase(
             updatedAt = now
         )
 
-        // Save to repository
-        val savedPlatz = platzRepository.save(platz)
+        // Upsert anhand des natürlichen Schlüssels (turnierId + name)
+        val savedPlatz = platzRepository.upsertByTurnierIdAndName(platz)
         return CreatePlatzResponse(
             platz = savedPlatz,
             success = true