feat(build): Refactor infrastructure modules and establish single source of truth

This commit introduces a major refactoring of the build system and the core infrastructure modules. The primary goal is to establish a strict "Single Source of Truth" for all dependencies using Gradle Version Catalogs and to create a clean, maintainable, and scalable foundation for all current and future services.

### 1. Centralized Dependency Management (`libs.versions.toml`)

- **Established Single Source of Truth:** All dependency versions are now exclusively managed in `gradle/libs.versions.toml`. Hardcoded versions have been removed from all build scripts.
- **Introduced Gradle Bundles:** To simplify module dependencies, several bundles have been created (e.g., `testing-jvm`, `redis-cache`, `spring-cloud-gateway`, `monitoring-client`). This drastically reduces boilerplate in the `build.gradle.kts` files and improves readability.
- **Cleaned up Aliases:** All library and plugin aliases have been standardized for consistency.

### 2. Infrastructure Module Refactoring

All infrastructure modules (`core`, `platform`, `auth`, `cache`, `event-store`, `messaging`, `monitoring`, `gateway`) have been refactored to align with the new dependency management strategy.

- **Simplified Build Scripts:** The `build.gradle.kts` for each module now uses the new bundles and aliases, making them significantly cleaner and easier to understand.
- **Consistent Structure:** The architecture of each module now clearly follows the Port-Adapter pattern where applicable (e.g., `cache-api`/`redis-cache`).
- **Standardized `platform-bom`:** The project's own Bill of Materials (`platform-bom`) now also includes the Spring Cloud BOM, ensuring version consistency for all Spring-related dependencies.

### 3. Added Infrastructure Documentation

To improve onboarding and architectural understanding, a dedicated `README-*.md` file has been created for each refactored infrastructure module:
- `README-CORE.md`
- `README-PLATFORM.md`
- `README-INFRA-AUTH.md`
- `README-INFRA-CACHE.md`
- `README-INFRA-EVENT-STORE.md`
- `README-INFRA-MESSAGING.md`
- `README-INFRA-MONITORING.md`
- `README-INFRA-GATEWAY.md`

These documents explain the purpose, architecture, and usage of each component within the system. This lays the groundwork for our "Tracer Bullet" development approach.

core/core-domain/build.gradle.kts

@@ -1,30 +1,23 @@
+// Dieses Modul definiert die Kern-Domänenobjekte des Shared Kernels.
+// Es enthält keine Implementierungsdetails, nur reine Datenklassen und Enums.
 plugins {
-    // KORREKTUR: Von JVM zu Multiplattform wechseln
-    alias(libs.plugins.kotlin.multiplatform)
+    alias(libs.plugins.kotlin.jvm)
     alias(libs.plugins.kotlin.serialization)
 }
 
-// KORREKTUR: Diesen Block hinzufügen, um die Ziele zu definieren
-kotlin {
-    jvm()
-    js(IR) {
-        browser()
-    }
+dependencies {
+    // Stellt sicher, dass dieses Modul Zugriff auf die im zentralen Katalog
+    // definierten Bibliotheken hat.
+    api(projects.platform.platformDependencies)
 
-    sourceSets {
-        val commonMain by getting {
-            dependencies {
-                // Die Abhängigkeiten kommen hier rein
-                api(projects.platform.platformDependencies)
-                api(libs.uuid)
-                api(libs.kotlinx.serialization.json)
-                api(libs.kotlinx.datetime)
-            }
-        }
-        val commonTest by getting {
-            dependencies {
-                implementation(projects.platform.platformTesting)
-            }
-        }
-    }
+    // Kern-Abhängigkeiten für das Domänen-Modell.
+    // `api` wird verwendet, damit Services, die `core-domain` einbinden,
+    // diese Typen ebenfalls direkt nutzen können.
+    api(libs.uuid)
+    api(libs.kotlinx.serialization.json)
+    api(libs.kotlinx.datetime)
+
+    // Stellt die Test-Bibliotheken bereit.
+    testImplementation(projects.platform.platformTesting)
+    testImplementation(libs.bundles.testing.jvm)
 }