CI quality gates (pre-merge checks)

Sets up the checks that gate a pull request before it merges to develop: the toolchain provisioning, then lint + format-check + type-check + test, with Jarvus's standard linters. The reusable core is the gate harness — provisioning, the script contract, path filters, lockfile-frozen installs — and linting is one tier that rides on it next to type-check and test.

The portfolio's actual failure mode isn't picking the wrong linter; it's repos that ship no linter at all (tests + type-check only, or build + test only). This skill exists so a new repo gets the whole gate by default instead of re-deciding — or skipping it.

Scope: what's in, what's out