chore: land dev -> main, retire ERAD-SP fork

[nikbott]

The dev→main reconciliation PR (was #2, then #8) was auto-closed twice — first by the cpp-sequential→dev rename, then by the data-protection history rewrite, which also severed dev's common ancestry with main. GitHub can't recreate it via API ("no history in common").

Since main is the superseded ERAD-SP fork and dev is canonical, the clean reconciliation is to make main equal dev (replace, not merge) — coordinate with @ronan, then e.g. git push origin dev:main (force, after agreement) or open the PR via the web compare UI with --allow-unrelated-histories at merge time.

Blocked on coordination with the collaborator.

[nikbott]

Update: the repo default branch is now dev (was the superseded main). This makes the canonical trunk primary for clones/PRs and surfaced the governance files (community-standards health 28% → 100%). main (Ronan's ERAD-SP fork) is untouched; the remaining step is deciding whether to replace/retire it — coordinate with @ronan.