refactor(frontend, build): update PingViewModel initialization, resolve view model via Koin, and clean yarn dependencies

Injected `PingViewModel` via Koin to align with dependency injection best practices. Suppressed Gradle deprecation warnings and added the `frontend.core.sync` dependency. Cleaned up outdated packages in `yarn.lock`.

contracts/ping-api/build.gradle.kts

@@ -27,6 +27,7 @@ kotlin {
     sourceSets {
         commonMain {
             dependencies {
+                implementation(projects.core.coreDomain)
                 implementation(libs.kotlinx.serialization.json)
             }
         }

contracts/ping-api/src/commonMain/kotlin/at/mocode/ping/api/PingData.kt

@@ -1,5 +1,6 @@
 package at.mocode.ping.api
 
+import at.mocode.core.sync.Syncable
 import kotlinx.serialization.Serializable
 
 @Serializable
@@ -21,3 +22,15 @@ data class HealthResponse(
     val service: String,
     val healthy: Boolean
 )
+
+/**
+ * Sync-Contract: Ping Event für Delta-Sync.
+ */
+@Serializable
+data class PingEvent(
+  // Using a String for the ID to be compatible with UUIDs from the backend.
+  override val id: String,
+  val message: String,
+  // Using a Long for the timestamp, which can be derived from a UUIDv7.
+  override val lastModified: Long
+) : Syncable