Admin write endpoints (SERVICE-scoped): arbitrary transfer, account rename/owner/archive, firm details

Backend tranche for the next batch of economy-explorer admin tools — extends the PAR-210 SERVICE-scoped, @Hidden admin surface with the ledger-authoritative mutations the UIs need. All gated by requireServiceKey, controller→service→mapper, server-side audited/logged, excluded from OpenAPI.

Endpoints

• POST /api/v1/admin/transfers — move money between arbitrary accounts with a memo. Reuse the extracted TransferService.executeTransfer(from,to,amount,memo,initiator,idempotencyKey,bypassAuthRequired); body {fromAccountId,toAccountId,amount,memo}, Idempotency-Key honoured. (Backs "move money between accounts with memo".)
• PATCH /api/v1/admin/accounts/{id}/display-name — rename any account (AccountMapper.updateAccountDisplayName, currently firm-scoped via FirmService). Validate ≤255.
• PATCH /api/v1/admin/accounts/{id}/owner — change accounts.owner_uuid_bin (new AccountMapper.updateOwner). Guard the uq_one_personal_per_player virtual unique index: refuse to set a PERSONAL account's owner to a player who already has one (mirror PAR-140's BUSINESS-account scope guard). Resolve owner by UUID or name (firm_players).
• POST /api/v1/admin/accounts/{id}/archive + /unarchive — AccountMapper.archiveAccount exists (set is_archived=1); add the unarchive (is_archived=0).
• PATCH /api/v1/admin/firms/{id} — set discord_url / hq_region (admin version of FirmController PATCH /firms/me; reuse FirmMapper.updateFirm, preserving display_name). (Backs "change business details like hq and discord".)

Notes

• Use the existing AdminFirmController/AdminFirmService pattern (or a sibling AdminAccountController/service). Keep @Hidden.
• executeTransfer already supports arbitrary from/to + bypassAuth; admin transfer should NOT bypass auth-required by default (that's a deliberate flag) — decide per endpoint; default false for the generic admin transfer, surface a clear error if an account requires an in-game authorizer.
• Tests in the AdminFirmServiceIT / embedded-MariaDB style: transfer between accounts, rename, owner change (incl. the personal-uniqueness guard), archive/unarchive round-trip, firm details update, and SERVICE-key gating (403 for non-SERVICE).

Consumed by the explorer admin tools (sibling Economy Explorer issues).