chore(build): update JVM target to 25, enforce stable kotlinx-serialization-json, and add bundle size budget checks

- Updated Kotlin compiler and JVM toolchain to target JVM 25 in all subprojects.
- Enforced stable `kotlinx-serialization-json:1.7.3` version to prevent resolution issues.
- Introduced JS bundle size budget checks for frontend shells with gzip support and reporting.
- Refined and reorganized Gradle module includes in `settings.gradle.kts`.
- Removed legacy and redundant dependency configurations for improved clarity.

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

@@ -5,7 +5,8 @@ plugins {
   alias(libs.plugins.kotlinSpring)
   alias(libs.plugins.kotlinJpa)
   alias(libs.plugins.spring.boot)
-  alias(libs.plugins.spring.dependencyManagement)
+  // FINALE BEREINIGUNG: Das `dependencyManagement`-Plugin wird entfernt.
+  // alias(libs.plugins.spring.dependencyManagement)
 }
 
 // Configure the main class for the executable JAR
@@ -14,10 +15,8 @@ springBoot {
 }
 
 dependencies {
-  // ULTIMATIVER TEST: Wir umgehen unser lokales BOM und importieren das offizielle Spring Boot BOM direkt.
-  // Wenn dies funktioniert, liegt der Fehler im Aufbau von `:platform:platform-bom`.
-  implementation(platform(libs.spring.boot.dependencies))
-  // implementation(platform(projects.platform.platformBom))
+  // Die `platform`-Deklaration ist der einzig korrekte Weg.
+  implementation(platform(projects.platform.platformBom))
 
   // Platform und Core Dependencies
   implementation(projects.platform.platformDependencies)