The controller now decides what a pull request's check runs from the mesh's module
graph, so the announcement carries the changed directories that hold a module at the
head and whether the head has a merge-check.sh. A verdict sets mesh/merge-gate (the
gate, with the modules it judged) and mesh/repo-check (the repository's own tests).
gitea_branch_protection_get/set let the operator's agent make those statuses required.
The catalogue's merge-check.sh leaves the gate to the build seat and keeps its own layer:
every manifest through module check, and the touched Go modules' tests.
