Derive the JUnit platform version from JUnit.version

[alexander-yevsyukov]

Problem

JUnit.Platform.version held the JUnit version as its own literal:

object JUnit : DependencyWithBom() {
    override val version = "6.1.3"
    ...
    object Platform : Dependency() {
        override val version: String = "6.1.3"   // repeated

Every JUnit bump therefore had to be applied twice. The latest bump to 6.1.3
was applied to both, but nothing enforced that — the two could drift silently,
and the platform artifacts would then be pinned off the BOM's line.

Fix

Read JUnit.version instead. JUnit.Jupiter.version already does exactly
this, so Platform now matches the sibling declared a few lines above it.

Why this is safe

JUnit 6 unified the platform and Jupiter version lines. Verified directly
against Maven Central: junit-bom:6.1.3 declares
junit-platform-launcher:6.1.3, and that artifact resolves (HTTP 200).

This was not true under JUnit 5, where the platform was 1.x while
Jupiter was 5.x. The KDoc now records that history, so the next reader does
not have to rediscover why tying the values together is correct now and would
have been a bug before.

No version changes: both sides were already 6.1.3.

Verification

• ./gradlew detekt — BUILD SUCCESSFUL.
• dependency-audit — APPROVE. It also confirmed there is no Kotlin
  object-initialization-order hazard in reading JUnit.version from the
  nested Platform object, and found no consumer reading
  JUnit.Platform.version directly.

Where this came from

Reported by Copilot on
jdbc-storage#183.
buildSrc/src/main/kotlin/io/spine/dependency/** is config-distributed, so
jdbc-storage only carries the overlay — the fix belongs here.

🤖 Generated with Claude Code

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-02T18:42:22.049674Z	105f78f	PR opened

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