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.

docs/05_Backend/Services/PingService.md

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+# Ping Service
+
+Der `ping-service` ist der "Tracer Bullet" Service für die Meldestelle-Architektur. Er dient als Blueprint für alle weiteren Microservices.
+
+## Verantwortlichkeit
+*   Technischer Durchstich (Frontend -> Gateway -> Service -> DB).
+*   Validierung der Infrastruktur (Security, Resilience, Observability).
+*   Referenzimplementierung für DDD, Hexagonal Architecture und KMP-Integration.
+
+## API Endpunkte
+
+| Methode | Pfad | Beschreibung | Auth |
+| :--- | :--- | :--- | :--- |
+| GET | `/ping/simple` | Einfacher Ping, speichert in DB | Public |
+| GET | `/ping/enhanced` | Ping mit Circuit Breaker Simulation | Public |
+| GET | `/ping/public` | Expliziter Public Endpoint | Public |
+| GET | `/ping/secure` | Geschützter Endpoint (benötigt Rolle) | **Secure** (MELD_USER) |
+| GET | `/ping/health` | Health Check | Public |
+| GET | `/ping/history` | Historie aller Pings | Public (Debug) |
+
+## Architektur
+Der Service folgt der Hexagonalen Architektur (Ports & Adapters):
+*   **Domain:** `at.mocode.ping.domain` (Pure Kotlin, keine Frameworks).
+*   **Application:** `at.mocode.ping.application` (Use Cases, Spring Service).
+*   **Infrastructure:** `at.mocode.ping.infrastructure` (Web, Persistence, Security).
+
+## Security
+*   Nutzt das zentrale Modul `backend:infrastructure:security`.
+*   OAuth2 Resource Server (JWT Validation via Keycloak).
+*   Rollen-Mapping: Keycloak Realm Roles -> Spring Security Authorities (`ROLE_...`).
+
+## Persistence
+*   Datenbank: PostgreSQL.
+*   Migration: Flyway (`V1__init_ping.sql`).
+*   ORM: Spring Data JPA (für Write Model).
+
+## Resilience
+*   Circuit Breaker: Resilience4j (für DB-Zugriffe und simulierte Fehler).