Decompose the 297-line run orchestrate() with the E10 port-lift #162

Severity: Low-medium (maintainability). Review finding D8; deferred by #157. Re-verified at 1c4e71e.

orchestrate in cmd/assent/run.go:175-471 is 297 lines and 10 numbered steps. It is well commented, and the emit-before-reconcile order is normative (D-122). The two gitlab.SyntheticDigest call sites inside it are the documented E10 collapse targets (AUD-S15 comment, around run.go:190-196).

Fix: decompose it as part of the E10 port-lift, not in a separate lane. Keep the D-122 order under the existing run tests. This issue exists so the decomposition is not forgotten when E10 lands.