chore(ping-service, security): integrate centralized security module and enhance Ping-Service

- Replaced local `SecurityConfig` in `ping-service` with the shared `infrastructure:security` module.
- Added `GlobalSecurityConfig` to standardize OAuth2, JWT validation, and CORS for all services.
- Introduced new endpoints (`/ping/public`, `/ping/secure`) with role-based access control.
- Updated database schema with Flyway migration (`V1__init_ping.sql`) and refactored persistence layer to align with the standardized approach (`createdAt` field).
- Enhanced application configuration (`application.yaml`) to use shared security and Flyway settings.

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

@@ -4,4 +4,8 @@ interface PingApi {
     suspend fun simplePing(): PingResponse
     suspend fun enhancedPing(simulate: Boolean = false): EnhancedPingResponse
     suspend fun healthCheck(): HealthResponse
+
+    // Neue Endpunkte für Security Hardening
+    suspend fun publicPing(): PingResponse
+    suspend fun securePing(): PingResponse
 }