Mint a STABLE, revocable public link to this call's recording.

Mirrors the get_recording_share_link MCP tool exactly — same shared mint_recording_share layer, same attendee guard (someone from the call's own account must have been on it, unless deliberately skipped), same gates, same call's-own-anchors stamping — minus the per-scope authorization: this is the staff surface, and minting is admin-only to match the External Links revoke. Guard refusal is a 409 whose detail the UI shows verbatim. Unanchored (unattributed/internal) calls are refused even with the skip — resolve first, so every live share stays attributable and scope-revocable. The minted link appears on /external-links.