Issue #3609113: Add an "Open" link to reach a parked step's interaction from the instance trace

Adds a generic hook_orchestra_ui_token_operations_alter(array &$links, TokenInterface $token) so a module can add its own per-token operations to the instance process trace.

orchestra_interaction implements it: a parked token whose node declares an interaction gets an "Open" link to the visitor's step page (carrying the per-step capability token), so an operator can reach the interaction from the trace to preview or resend it.

To build the link as a render element, InteractionUrlsInterface gains stepLink() returning a Url (same target as stepUrlForToken(), which now delegates to it); the capability and assignment gateways implement it.

Covered by a new kernel test (InteractionOperationsTest): the link is added for a parked interactive token and withheld for a plain one.

Closes #3609113.