create-release and add-doi: sync dev with main after release commits

[larnsce]

Observed on solidwastekampala v1.0.0.

Both the create-release and the add-doi skill commit and push to main only. In openwashdata repositories the default branch on GitHub is dev, and GitHub reads CITATION.cff from the default branch for the repository page and the "Cite this repository" widget. After a release, GitHub therefore keeps showing the pre-release citation (old version, no DOI) even though main is correct. In solidwastekampala, dev still showed version 0.0.0.9000 with no DOI after the v1.0.0 release and the DOI integration.

Fix: add a final step to both skills that syncs dev after the release commits land on main.

git push origin main:dev

The push is a fast-forward when dev has no commits that main lacks, which is the normal state right after a release. If the push is rejected because dev moved ahead in the meantime, the step should fall back to merging main into dev and pushing.

Placement: after Step 4 (commit and release) in create-release, and after Step 6 (verify) in add-doi. Since create-release Step 5 delegates to add-doi, putting the sync at the end of add-doi covers the combined flow, and create-release only needs it for the release commit itself.

[larnsce]

Follow-up from the same release: the stale citation on GitHub had a second cause. The default branch of solidwastekampala was dev, so GitHub read CITATION.cff, the README, and the "Cite this repository" widget from dev even though main was correct. GitHub makes the first branch pushed at repository creation the default, so any package whose development started on dev has this state.

The fix for the skills should therefore have two parts:

1. Check the default branch and set it to main if it is not (gh repo edit --default-branch main). A one-time check, best placed in create-release Step 1.
2. Keep the git push origin main:dev sync described above, so dev does not drift behind main between releases.

For solidwastekampala the default branch is now main and dev is synced to main.

[larnsce]

Folded into the release skills on dev (be5cb26): create-release Step 1 checks the GitHub default branch and sets it to main on the user's yes, Step 4 pushes main:dev after the release commit (merge fallback when dev moved ahead); add-doi Step 9 repeats the sync after the DOI commit, which also covers the combined flow through create-release Step 5. Closes on the v1.5.0 release merge (#68).

[larnsce]

Shipped in pkgreview v1.5.0: PR #70 merged into main (be4d23c), tag v1.5.0 on the merge commit, dev fast-forwarded to main. In-flight reviews stamped 1.4.0 or earlier keep fetching their pinned checklists and org profiles.