build(deps): secure Dokka Jackson classpath

[jbeckwith-oai]

Summary

• align every Jackson module on Dokka-only Gradle configurations to 2.18.9
• keep the SDK's published Jackson dependency at 2.18.9
• keep the lower 2.14.0 Jackson compatibility test unchanged

This is stacked on #791, which upgrades the build-only Dokka plugin to 2.1.0 while preserving the existing documentation pipeline and links.

Why

Dokka 2.1.0 declares Jackson 2.15.3. Its Gradle plugin creates Jackson-bearing GFM, HTML, Javadoc, and Jekyll plugin/runtime configurations across the root project and every subproject. In openai-java-core, the SDK compatibility rule also previously forced some of those build-tool configurations down to 2.14.0.

The new rule applies only to configuration names beginning with dokka. A full configuration scan found 110 Jackson-bearing Dokka configurations; all 110 now resolve the complete Jackson family to 2.18.9 with zero mismatches or resolution failures. SDK compile, test, runtime, and publication configurations are outside this rule.

This removes Dokka build-classpath paths for Dependabot alerts 58, 94, 96, 98, and 100. Alerts that also observe the intentional 2.14.0 compatibility-test classpath may remain open; raising that compatibility floor would be a separate downstream-compatibility decision.

Compatibility

• all four published Maven POMs are byte-for-byte identical to the refreshed build(deps): update Dokka to 2.1.0 #791 parent
• Gradle module metadata is semantically identical; only regenerated artifact checksums differ
• production and source JAR entry contents are identical
• Javadoc JAR entry lists and artifact names are identical
• the 9,691-file aggregate Javadoc tree is byte-for-byte identical
• internal Javadoc link references and targets are unchanged
• every published class remains Java 8 bytecode (class major version 52)
• Dokka and its Jackson classpath remain build-only and do not appear in published metadata

Validation

• all 110 Jackson-bearing Dokka configurations resolve only Jackson 2.18.9
• ./scripts/lint
• ./scripts/build
• ./scripts/test
• ./scripts/detect-breaking-changes origin/codex/update-dokka
• ./gradlew clean publish -PpublishLocal --no-configuration-cache
• aggregate Dokka Javadoc generation
• GFM, HTML, Javadoc, and Jekyll collector/multimodule classpath resolution
• before/after comparison of POMs, Gradle module metadata, production/source JAR contents, Javadoc entries, aggregate Javadocs, internal links, and class-file versions