feat: add Kotlin SDK BOM

[original4422]

Summary

• add a publishable kotlin-sdk-bom Java platform
• constrain kotlin-sdk-core, kotlin-sdk-client, and kotlin-sdk-server to the project version
• document importing the BOM and using versionless SDK dependencies

The module reuses the existing mcp.publishing convention, so its POM carries the same Maven Central metadata and signing setup as the other SDK artifacts. It publishes platform metadata and a POM, not a runtime JAR.

Fixes #351

Validation

• ./gradlew :kotlin-sdk-bom:clean :kotlin-sdk-bom:build :kotlin-sdk-bom:generatePomFileForMavenPublication ktlintCheck detekt apiCheck --stacktrace --continue
• published the BOM to an isolated Maven repository and verified that an external Gradle consumer resolves all three versionless SDK modules to 0.15.0
• ./gradlew jvmTest :conformance-test:build :docs:build :kotlin-sdk-bom:build --max-workers 3 --continue

A broader ./gradlew build --max-workers 3 --continue --rerun-tasks completed the JVM suites and platform compilation until Apple native link tasks required Xcode, which is not installed in this environment (xcrun xcodebuild -version exits 72). Those Apple link tasks are left to macOS CI.

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[original4422]

Hi @devcrocod, when you have a chance, would you mind reviewing this BOM artifact change and letting me know if any changes are needed? Thank you!

[original4422]

Hi @devcrocod, following up since the last review request—when you have a chance, could you please take another look and let me know whether this is ready to merge or needs changes? Thanks!