Warn when 'Return to the workflow after submit' is used with an inline/modal confirmation type

The webform resume handler's "Return to the workflow after submit" setting (return_to_workflow) redirects the visitor to the interaction dispatcher in the handler's confirmForm(). Webform runs handler confirmForm() after setConfirmation(), so the redirect only takes effect when the webform's confirmation type performs a redirect the handler can then override.

With the inline (and modal) confirmation type, setConfirmation() calls setRebuild() and re-renders the form in place, which swallows the handler's redirect: the visitor is left on the webform's own confirmation instead of being sent to the next step. Chaining silently does nothing, and the misconfiguration is easy to make.

Proposed: in OrchestraResumeHandler::validateConfigurationForm(), when return_to_workflow is enabled and the webform's confirmation type is inline or modal, set a non-blocking warning that tells the author to use a redirecting confirmation type (for example Page). Non-blocking because every other confirmation type works and the author may be mid-edit.

Also note the constraint in docs/interaction.md and cover it with a test assertion.