Define the required code and commit rules

The skills set declaration order, owning test filenames, multiline
separators, and explicit handling of ignored errors. Review covers the
rules that the current checks do not enforce, so a tool pass does not
stand for full style compliance.

Every commit uses the configured signing key and needs cryptographic
verification. Code and issue pushes need permission, as does a rewrite
of published history, so routine steps do not imply that consent.

Issue: 3cdc678