chore: prepare workflows for 3.x line

[ewaostrowska]

Pull Request

Workflow changes

• codeql-analysis.yml: Run on pushes and pull requests to 3.0.0. Use a JDK 17 Maven cache key. The scheduled scan remains in the file; GitHub runs scheduled workflows from the default branch.
• maven.yml: Run the build and snapshot deployment workflow on pushes to 3.0.0. Rename the workflow to Build Test Deploy 3.0.0. The existing Java 17, 21, and 25 build matrix remains, with snapshot deployment on Java 17.
• prepare-release.yml: Set the prepare-release pull request base to the branch selected for the manual run. The workflow now uses that branch instead of an implicit default base.
• release.yml: Check out the branch selected for the manual run after publishing Javadocs. Create the next-snapshot pull request against that branch. Remove the steps that update the 1.5 README and the 2.x Wiki.
• maven-v1.yml and maven-v1-pulls.yml: Remove the 1.5 push and pull request workflows from the 3.0.0 branch. The 1.5 branch has its own copies.

Script changes

• CI/lastRelease.py: Find the latest published v3 release. If none exists, use the latest published v2 release and print a warning.
• CI/releaseNotes.py: List pull requests merged into 3.0.0 and create the draft GitHub release from that branch.
• CI/publishRelease.py: Publish the GitHub release with 3.0.0 as its target branch.
• CI/prepare-release.sh: Update dependency examples in the main README and plugin READMEs to the new release version. Remove the old step that added a release row to the main README.
• CI/post-release.sh: Stop copying the scripts for 1.5 README and 2.x Wiki updates. The release workflow no longer runs them.
• CI/update-v1-readme.sh and CI/update-wiki.sh: Remove these scripts from the 3.0.0 branch because its release does not update the 1.5 README or the 2.x Wiki.
• CI/test.py: Remove an unused copy of the release notes script.

Documentation

• Update the CI guide for the 3.x release steps and fix the README build badge name.

Type of Change

• 🐛 Bug fix
• ✨ New feature
• ♻️ Refactor (non-breaking change)
• 🧪 Tests
• 📝 Documentation
• 🧹 Chore (build or tooling)

Checklist

• I have added/updated tests as needed
• I have added/updated documentation where applicable
• The PR title is descriptive
• The code builds and passes tests locally
• I have linked related issues (if any)

Screenshots / Additional Context