[feat] Automate brownfield gradle plugin releases

[adamTrz]

Summary

This PR automates Maven Central publication for the Brownfield Gradle Plugin and removes the manual local-zip upload process.

It adds:

• a dedicated GitHub Actions workflow triggered by brownfield-gradle-plugin/v* tags and workflow_dispatch
• repo-root JReleaser configuration for GitHub release creation and Maven Central publication
• a plugin version sync/check script for release-related consumers
• a plugin-scoped release notes generator based on git history
• updated maintainer publishing documentation

Why

The plugin was previously published manually by signing and publishing to mavenLocal(), zipping the com/ subtree, and uploading it manually to Maven Central. That flow was slow, error-prone, and had no release-notes automation.

Impact

Maintainers can now:

• publish on a dedicated plugin tag push
• run a safe workflow_dispatch dry run that generates notes and stages Maven artifacts without publishing
• rely on one source of truth for the plugin version in gradle-plugins/react/brownfield/gradle.properties

Developers keep the existing local snapshot path for CI and local Android testing via mavenLocal().

Validation

Validated in an isolated worktree on top of origin/main.

Passed locally:

• node --test --experimental-strip-types scripts/__tests__/sync-brownfield-gradle-plugin-version.test.ts
• node --test --experimental-strip-types scripts/__tests__/generate-brownfield-gradle-plugin-release-notes.test.ts
• yarn brownfield:plugin:version:check
• yarn brownfield:plugin:release-notes --version 1.1.0 --ref HEAD --output /private/tmp/bgp-release-notes.md
• ruby -e 'require "yaml"; YAML.load_file(".github/workflows/release-brownfield-gradle-plugin.yml"); YAML.load_file("jreleaser.yml"); puts "yaml ok"'
• git diff --check
• cd gradle-plugins/react && ./gradlew :brownfield:publishMavenLocalPublicationToReleaseStagingRepository -PSkipSigning=true
• local signed publish to Maven Local succeeded: yarn brownfield:plugin:publish:local:signed
• local signed release staging succeeded: cd gradle-plugins/react && ./gradlew :brownfield:publishMavenLocalPublicationToReleaseStagingRepository
• staged release artifacts include .asc signatures for jar, sources jar, javadoc jar, module metadata, and pom
• repo hooks on commit: typecheck, lint, commitlint

Passed remotely before removing the temporary PR-only trigger used for pre-merge validation:

• GitHub Actions run 26442399021 on PR #351
• Validate release inputs and stage artifacts passed
• Publish Brownfield Gradle Plugin was skipped intentionally
• artifacts uploaded successfully:
  • brownfield-gradle-plugin-release-notes
  • brownfield-gradle-plugin-staging-repo

Still not executed remotely:

• GitHub Actions workflow_dispatch dry run after merge to main
• JReleaser publish path against GitHub/Maven Central services