feat(horses-service): remove legacy configuration and repository classes

- Deleted outdated `ApplicationConfiguration` and `HorseRepositoryImpl` classes.
- Migrated to streamlined modular Gradle configuration in `build.gradle.kts`.
- Updated domain models and dependencies to use multiplatform and serialization plugins.
- Added modular setup for `horses` namespace in `settings.gradle.kts`.
- Reorganized database configuration with minimal JDBC bindings for development.

Signed-off-by: Stefan Mogeritsch <stefan.mo.co@gmail.com>

backend/services/clubs/clubs-domain/build.gradle.kts

@@ -0,0 +1,26 @@
+plugins {
+  alias(libs.plugins.kotlinMultiplatform)
+  alias(libs.plugins.kotlinSerialization)
+}
+
+kotlin {
+  jvm()
+
+  sourceSets {
+    commonMain {
+      kotlin.srcDir("src/main/kotlin")
+      dependencies {
+        implementation(projects.core.coreDomain)
+        implementation(projects.core.coreUtils)
+        implementation(libs.kotlinx.datetime)
+        implementation(libs.kotlinx.serialization.json)
+      }
+    }
+    commonTest {
+      kotlin.srcDir("src/test/kotlin")
+      dependencies {
+        implementation(projects.platform.platformTesting)
+      }
+    }
+  }
+}

backend/services/clubs/clubs-domain/src/main/kotlin/at/mocode/clubs/domain/model/DomClub.kt

@@ -0,0 +1,38 @@
+@file:OptIn(kotlin.uuid.ExperimentalUuidApi::class)
+
+package at.mocode.clubs.domain.model
+
+import at.mocode.core.domain.model.DatenQuelleE
+import at.mocode.core.domain.serialization.KotlinInstantSerializer
+import at.mocode.core.domain.serialization.UuidSerializer
+import kotlinx.serialization.Serializable
+import kotlin.time.Clock
+import kotlin.time.Instant
+import kotlin.uuid.Uuid
+
+/**
+ * Domain model representing a club (Verein) in the registry system.
+ *
+ * @property clubId Unique internal identifier (UUID).
+ * @property vereinsNummer ÖPS club number (from ZNS VEREIN01.dat).
+ * @property name Club name.
+ * @property datenQuelle Source of the data.
+ * @property createdAt Timestamp when this record was created.
+ * @property updatedAt Timestamp when this record was last updated.
+ */
+@Serializable
+data class DomClub(
+  @Serializable(with = UuidSerializer::class)
+  val clubId: Uuid = Uuid.random(),
+
+  val vereinsNummer: String,
+  val name: String,
+
+  val istAktiv: Boolean = true,
+  val datenQuelle: DatenQuelleE = DatenQuelleE.IMPORT_ZNS,
+
+  @Serializable(with = KotlinInstantSerializer::class)
+  val createdAt: Instant = Clock.System.now(),
+  @Serializable(with = KotlinInstantSerializer::class)
+  var updatedAt: Instant = Clock.System.now()
+)