refactor(ping-service): remove CORS configuration from code, restructure modules, and update Gradle dependencies

Migrated CORS settings from code to `application.yaml` for better separation of concerns. Integrated `ping-api` into the new `contracts` module for improved modularity. Updated Gradle scripts and dependencies accordingly to reflect the new project structure.

settings.gradle.kts

@@ -28,6 +28,11 @@ dependencyResolutionManagement {
   }
 }
 
+// ==========================================================================
+// CONTRACTS
+// ==========================================================================
+include(":contracts:ping-api")
+
 // ==========================================================================
 // Backend
 // ==========================================================================
@@ -89,7 +94,6 @@ include(":backend:services:entries:entries-service")
 // include(":backend:services:members:members-service")
 
 // --- PING (Ping Service) ---
-include(":backend:services:ping:ping-api")
 include(":backend:services:ping:ping-service")
 
 // --- REGISTRY (Single Source of Truth) ---