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.

gradle/libs.versions.toml

@@ -160,6 +160,9 @@ spring-security-oauth2-jose = { module = "org.springframework.security:spring-se
 spring-web = { module = "org.springframework:spring-web" }
 springdoc-openapi-starter-common = { module = "org.springdoc:springdoc-openapi-starter-common", version.ref = "springdoc" }
 springdoc-openapi-starter-webmvc-ui = { module = "org.springdoc:springdoc-openapi-starter-webmvc-ui", version.ref = "springdoc" }
+# KORREKTUR: WebFlux-Variante von SpringDoc hinzugefügt.
+springdoc-openapi-starter-webflux-ui = { module = "org.springdoc:springdoc-openapi-starter-webflux-ui", version.ref = "springdoc" }
+
 
 # --- Spring Cloud ---
 spring-cloud-starter-gateway-server-webflux = { module = "org.springframework.cloud:spring-cloud-starter-gateway-server-webflux" }