feat(audit): archive retention and superseded stale-archive cleanup (ScadaBridge#109)

Owner decisions recorded: the archive destination stays a directory/UNC
(no object-storage client; share + permissions named at enablement),
parquet-tools-only reading (no re-import), unsigned like the chain (#107).

AuditLog:Archive:RetentionDays (default 0 = never delete; else must exceed
AuditLog:RetentionDays, counted from the archived month's end) and
DeleteSupersededStaleArchives (default true) run after every purge tick.
A retried purge's stale Archived archive is deleted only when a later,
verifying, Purged archive of the same partition provably holds every row:
same prior anchor and the stale chain-end hash at its chain-end sequence
(row or tombstone), every unchained row present by EventId; otherwise it is
reported KeptStale. A sole copy left at Archived is never touched. Deletion
removes only the archive name's own three files in its folder, manifest
first, never a manifest-supplied path. `audit archive cleanup [--dry-run]`
= CleanupAuditArchives (Administrator).

AuditLogArchiveCleanupTests (MSSQL) cover retried purge, kept stale copy,
sole copy, retention and the path guard; each safety rule mutation-checked.
Follow-ups filed: #113, #114, #115.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

docs/requirements/Component-ManagementService.md

@@ -202,6 +202,7 @@ The two-person authorization workflow for writes through the MxAccess Gateway. B
 - **VerifyAuditChain** (ScadaBridge#41): verifies one UTC calendar month (`Month`, `YYYY-MM`) of the central AuditLog hash chain and returns an `AuditChainVerificationResult` (status, rows verified, tombstones applied, purge anchor, head sequence, unchained rows, first break with partition / `ChainSeq` / `EventId` / kind). Gated on the OperationalAudit roles (`Administrator`, `Viewer`); a site-scoped non-Administrator caller is refused (`ManagementUnauthorized`) because a month's chain spans every site. Long-running Ask timeout. Errors: `INVALID_ARGUMENT` (bad month), `CHAIN_BUSY` (a chaining/purge pass held the chain lock past 60 s). Backs `scadabridge audit verify-chain`.
 - **VerifyAuditChainHeads** (ScadaBridge#107): checks chain heads exported off-box (`Records`, at most 50,000 `AuditChainHeadRecord`s; duplicates collapsed) against the database chain and returns an `AuditChainHeadVerificationResult` (overall `Verified`, one `AuditChainHeadCheck` per distinct exported head: `Matches` / `Extended` / `Purged`, or the failures `Mismatch` / `Regressed` / `MissingHead` / `MissingLink` / `CountMismatch`). Same gate as VerifyAuditChain; long-running Ask timeout. Errors: `INVALID_ARGUMENT` (no records / over the cap), `CHAIN_BUSY`. Backs `scadabridge audit verify-heads`.
 - **ListAuditArchives** / **VerifyAuditArchive** (ScadaBridge#42): list the AuditLog Parquet cold archives under `AuditLog:Archive:Directory` (`AuditArchiveListResult`: enabled flag + every manifest), and verify one by `Name` (`AuditArchiveVerificationResult`: file integrity, per-month chain recomputed from the archived rows, anchor `Matches`/`Superseded`/`NotPurged`/`Mismatch`, overall `Verified`). Same gate as VerifyAuditChain (OperationalAudit roles, site-scoped non-Administrator refused). VerifyAuditArchive uses the long-running Ask timeout. Errors: `ARCHIVE_NOT_CONFIGURED`, `INVALID_ARGUMENT` (not an archive name), `NOT_FOUND`. Back `scadabridge audit archive list|verify`.
+- **CleanupAuditArchives** (ScadaBridge#109): runs the archive cleanup now (`DryRun` = report only) — superseded stale archives a later purged archive provably covers, and archives past `AuditLog:Archive:RetentionDays` — and returns an `AuditArchiveCleanupResult` (`DryRun`, `RetentionDays`, one item per archive deleted / kept stale, with the action `DeletedExpired` / `DeletedSuperseded` / `KeptStale` and reason). Administrator only; runs on the maintenance-connection archive when registered; long-running Ask timeout. Errors: `ARCHIVE_NOT_CONFIGURED`. Backs `scadabridge audit archive cleanup`.
 
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