🚚 Update remaining master references to main

[alecgibson]

The default branch is now main. GitHub retargeted the open pull requests, moved the Pages build branch, and redirects web and API requests for the old name, so what's left is the references we hard-code ourselves.

The master entry in both workflows' branches: filters was only there to keep CI matching across the rename. It matches nothing now, so it goes.

gh_edit_branch in docs/_config.yml is what just-the-docs builds the "Edit this page on GitHub" footer link from, on every docs page. Web redirects cover a stale value for now, but they're not worth relying on long term.

The Coveralls badge takes ?branch=main in both its image and its link. The Test badge moves to the per-workflow URL, which accepts a branch parameter, so it reads consistently with the Coveralls badge beside it. This one is a trade-off rather than a straight improvement: the old /workflows/Test/badge.svg form implicitly tracked whatever the default branch happened to be, so it would have survived this rename — and any future one — untouched, where the pinned form won't.

Left alone deliberately: coverallsapp/github-action@master and the ottypes/json1 links name branches in other repositories, and GitHub explicitly doesn't redirect uses: refs.

Coveralls still has master as the project's default branch in its own settings, which we can't change from here, so the coverage badge will read as unknown until a build reports on main.

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com

[coveralls]

coverage: 97.485%. remained the same — update-master-references-to-main into main