chore: add GitHub Actions workflows for CI, snapshots, and releases

[deer]

Adds three GitHub Actions workflows:

• main-pull-request.yml — builds and tests every PR targeting main (./mvnw clean install, Java 25 Zulu)
• publish-snapshot.yml — publishes a snapshot to Maven Central on every push to main, and on manual trigger
• release.yml — manual workflow that sets the release version, builds and deploys to Maven Central, tags the commit, bumps to the next development version, and opens a PR back to main; release and next versions can be overridden via inputs or derived automatically from the current POM version

[deer]

The JDKDetector was causing problems but is doing its job:

[INFO] Running build.spawn.platform.local.jdk.JDKDetectorTests
Path: /opt/hostedtoolcache/Java_Zulu_jdk/25.0.2-10/x64
Path: /opt/hostedtoolcache/Java_Temurin-Hotspot_jdk/25.0.2-10/x64
Path: /opt/hostedtoolcache/Java_Temurin-Hotspot_jdk/17.0.18-8/x64
Path: /opt/hostedtoolcache/Java_Temurin-Hotspot_jdk/21.0.10-7/x64
Path: /opt/hostedtoolcache/Java_Temurin-Hotspot_jdk/11.0.30-7/x64
Path: /opt/hostedtoolcache/Java_Temurin-Hotspot_jdk/8.0.482-8/x64
Current JDK{version=25.0.2, home=/opt/hostedtoolcache/Java_Zulu_jdk/25.0.2-10/x64}
Detected Default JDK: JDK{version=25.0.2, home=/opt/hostedtoolcache/Java_Zulu_jdk/25.0.2-10/x64}
Detected JDK{version=8.0.482, home=/opt/hostedtoolcache/Java_Temurin-Hotspot_jdk/8.0.482-8/x64}
Detected JDK{version=11.0.30, home=/opt/hostedtoolcache/Java_Temurin-Hotspot_jdk/11.0.30-7/x64}
Detected JDK{version=17.0.18, home=/opt/hostedtoolcache/Java_Temurin-Hotspot_jdk/17.0.18-8/x64}
Detected JDK{version=21.0.10, home=/opt/hostedtoolcache/Java_Temurin-Hotspot_jdk/21.0.10-7/x64}
Detected JDK{version=25.0.2, home=/opt/hostedtoolcache/Java_Zulu_jdk/25.0.2-10/x64}