Application callback for workflow_stem.

Bridges workflow_stem's adapter configuration into mobus_stepwise's application env so the foundation engine's Mobus.Stepwise.Capabilities module sees the correct adapter. This keeps consumer-facing config under the :workflow_stem key while the foundation reads from :mobus_stepwise.

Startup-only bridging

Bridging happens once at application start. If a consumer changes adapter config at runtime via Application.put_env(:workflow_stem, ...), call rebridge/0 to propagate the change to mobus_stepwise's env. Test helpers and interactive development are the primary use cases; production config is typically set at compile/startup.

Defaults

:capability_runner_strict defaults to true (unlike the foundation's false). Rationale: workflow_stem consumers always configure a capability runner adapter, so a nil adapter signals a misconfiguration. The test helper at test/test_helper.exs sets this explicitly so tests are self-documenting.