chore(build, docs): add security module and update infrastructure decisions

- Created `backend/infrastructure/security` module with standardized configurations for OAuth2, JWT validation, CORS, and role mapping.
- Updated ADRs to reflect resolved backend infrastructure decisions, including security standardization, persistence strategy, and Flyway schema location.
- Enabled integration of the `security` module into relevant projects (e.g., `ping-service` and `gateway`).

backend/services/ping/ping-service/build.gradle.kts

@@ -19,8 +19,10 @@ dependencies {
     // Our central BOM for consistent versions
     implementation(platform(projects.platform.platformBom))
     implementation(projects.platform.platformDependencies)
-    // NEU: Zugriff auf die verschobenen DatabaseUtils
+
+    // Infrastructure Modules
     implementation(projects.backend.infrastructure.persistence)
+    implementation(projects.backend.infrastructure.security) // NEU: Security Module
 
     // === Spring Boot & Cloud ===
     // Standard dependencies for a secure microservice