[hp-himani]

Closes #112

Changes

• Keep the full clean-repo check, as discussed in the issue, but report what differs instead of a generic sentence.
• Add a separate branch check before the clean check. It explains the expected vs. found remote branch and how to fix it (switch branch, --branch, or releasify config --arg branch).
• Add a message for a branch that tracks no remote branch (tracking is null), suggesting git push -u <remote> <branch>.

Before / after

Before (older Node.js):

The git repo must be clean (committed and pushed) before releasing!

After, with a modified file:

The git repo must be clean (committed and pushed) before releasing!
- modified: ["package.json"]
- files: [{"path":"package.json","index":" ","working_dir":"M"}]
Check "git status", then commit, push or pull before trying again.

After, with the wrong tracked branch:

Your local branch tracks "origin/master", but releasify expects "origin/main".
Either switch to the branch you want to release, or tell releasify which one to use:
- for this run only: add --branch <name> (and --remote <name> if needed)
- as your new default: run "releasify config --arg branch"

Testing

• New tests: wrong tracked branch, no tracked branch, and the fields listed in
  the dirty-repo error.
• npm test: 63/63 pass, 100% coverage. npm run lint: clean.