Adds the gate workflow + check script + Krystie public key under .gitea/.
This commit is intentionally unsigned so the gate treats it as an admin
bootstrap rather than a Krystie commit (which the gate would otherwise
require to land via krystie-wip/* + auto-merge).
After this, master branch protection will be enabled requiring the
Krystie Gate workflow to pass on all future pushes. Krystie will push
to krystie-wip/<task-id> branches and the workflow auto-merges on green.
See: krystie-buildout/workflows/* in the krystie repo for sources.
sami7777