feat(sei-agent-driver): set the review's reasoning effort per session - #468

Since the last review, a new test covers clearing effort on an adopted session (TestAdoptedSessionsEffortIsClearedWhenNoneIsConfigured), using a generalised adoptFakeServer, which closes the test gap I raised last time; the earlier config.go:242 thread is already resolved and holds. Nothing blocks; I kept codex's one finding that the clear assertion is loose, as a nit, since with an empty want only the clear path can run and the test can only miss a wrong alias value (reviewed against the PR tree at c0d27f4; Go is not installed here, so the tests were not run).