This repository's default branch is main, but every workflow was still keyed to
master, so none of them could ever run:
- build-and-test.yml triggered on push/PR to master, so CI never fired and the
README's build badge had no status to report.
- docker-publish.yml keyed off a successful build-and-test run on master, so it
never fired either. Only trigger filters and comments referenced the branch;
the tag-vs-branch logic was already branch-agnostic.
- make-release.yml actively refused to run, failing with "Regular releases can
only be created from the 'master' branch."
Also updated the branch names throughout docs/DEVELOPMENT_WORKFLOW.md to match.