Wipe discovery/tracking data and re-run discovery.

Saves admins from the four-step manual flow (reset → impersonate → continue → approve in tracking) when re-running discovery is the goal. Behaves like reset-to-sources for the wipe, then immediately spawns a new discovery execution as the claim creator. By default re-uses claim.discovery_prompt verbatim; if payload.prompt is supplied it overwrites the stored prompt before discovery is spawned (empty string is allowed).