Fix Maven Central publishing: add missing sbt-sonatype plugin

[Copilot]

build.sbt referenced localStaging.value and sonaUpload from sbt-sonatype plugin without declaring the plugin dependency, breaking Maven Central publishing.

Changes

• project/plugins.sbt: Added sbt-sonatype 3.12.2
• build.sbt:
  • Configured sonatypeCredentialHost := sonatypeCentralHost for Sonatype Central Portal
  • Updated publishTo to use sonatypePublishToBundle.value (replaces deprecated localStaging.value)
  • Updated ci-publish command to use sonatypeBundleRelease (replaces deprecated sonaUpload)

Publishing flow

Releases (BUILD_RELEASE=true):

1. publishSigned → local bundle staging at target/sonatype-staging/<version>/
2. sonatypeBundleRelease → upload bundle to Central Portal, auto-close and release

Snapshots: Direct publish to https://central.sonatype.com/repository/maven-snapshots/

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• www.scala-sbt.org
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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