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.

platform/platform-dependencies/build.gradle.kts

@@ -1,3 +1,5 @@
+/*
+// Multiplatform
 plugins {
     alias(libs.plugins.kotlin.multiplatform)
 }
@@ -11,12 +13,6 @@ kotlin {
     sourceSets {
         val commonMain by getting {
             dependencies {
-                // KORREKTUR: Die explizite `platform()`-Abhängigkeit wird hier entfernt.
-                // Die Versionen aus der BOM werden trotzdem angewendet.
-
-                // KORREKTUR: `stdlib` und `reflect` werden entfernt.
-                // `stdlib` wird automatisch hinzugefügt.
-
                 api(libs.kotlinx.coroutines.core)
                 api(libs.kotlinx.serialization.json)
                 api(libs.kotlinx.datetime)
@@ -25,11 +21,30 @@ kotlin {
 
         val jvmMain by getting {
             dependencies {
-                api("org.jetbrains.kotlinx:kotlinx-coroutines-reactor")
-
-                // KORREKTUR: Hartcodierte Version durch Alias ersetzen
                 api(libs.kotlin.logging.jvm)
+                api(libs.kotlinx.coroutines.reactor)
             }
         }
     }
 }
+*/
+
+// Dieses Modul ist ein reines "Sammelmodul".
+// Es hat keinen eigenen Code, sondern bündelt nur gemeinsame Laufzeit-Abhängigkeiten,
+// die von den meisten JVM-Modulen benötigt werden.
+plugins {
+    alias(libs.plugins.kotlin.jvm)
+}
+
+dependencies {
+    // Importiert die zentrale BOM, um konsistente Versionen zu gewährleisten.
+    api(platform(projects.platform.platformBom))
+
+    // Stellt die wichtigsten Kotlin(x)-Bibliotheken via `api` bereit,
+    // damit jedes Modul, das von `platform-dependencies` abhängt, diese automatisch erhält.
+    api(libs.kotlinx.coroutines.core)
+    api(libs.kotlinx.serialization.json)
+    api(libs.kotlinx.datetime)
+    api(libs.kotlin.logging.jvm)
+    api(libs.kotlinx.coroutines.reactor)
+}