Let a proposed record be withdrawn (issue 1081)

A dropped proposal or a stale reservation stayed proposed forever: there was
no way to say the operator decided against it. knowledge-base.withdraw takes
a reserved or proposed record to withdrawn as a new version naming why, ends
a waiting operator's ask and clears a pending review in the same version,
and refuses an already accepted, superseded or withdrawn record. The number
stays spent either way.

The old Withdraw (the background job for reservations never proposed) is
renamed WithdrawStale to make room for the new, caller-driven WithdrawRecord.

modules/mesh-knowledge/README.md

@@ -26,6 +26,7 @@ operator, it is accepted only on the operator's Approve, given on a channel that
 | `propose` | the record whole | proposed, or refused naming every rule it breaks; an accepted record changes only by a progressive insight (`insight`), but an active research effort takes new versions freely, each reviewed as a proposal. Each version proposed is then reviewed by the knowledge base itself (below) |
 | `import` | `dry-run`, `commit` | hq's decision records and research efforts at the commit the records module stands at, each whole at its own number |
 | `return` | `number`, `reason` | drafted clauses sent back to be drafted again; refused for a record whose clauses another record changed or links by number |
+| `withdraw` | `number`, `kind`, `why` | a reserved or proposed record withdrawn, as a new version naming why; its number stays spent. A pending review is cleared and a waiting operator's ask is ended. Refused for a record already accepted, superseded or withdrawn |
 
 `ask`, `get`, `holds` and `history` stay within `bound` bytes (4096 unless asked for, at most 65536) and say what they cut
 and how to read the rest. The module's own tool `knowledge_health` answers its health (below).