Retire Median's QuickBooks statement account for an account made inactive in QuickBooks (#3489)

Marks Median's own institution "QuickBooks" statement account (no provider, integration or external id) disconnected, requiring immutable creation-mapping provenance recorded when the materializer inserted the row. Unverified legacy or manual rows return 422 QUICKBOOKS_STATEMENT_ACCOUNT_PROVENANCE_UNVERIFIED; labels, timestamps and matching shape do not establish provenance, and this endpoint cannot recover it. The GL account can then be separately deactivated through chart-of-accounts/{accountId}/deactivate, subject to its guards, including posted lines in an open period even at zero net balance. Allowed only while every current mapping to that GL account is a QuickBooks Bank or Credit Card account that the latest completed read found inactive. The row and its reconciliations are kept; the change and the reason are audited with the actor (and, for the agent service token, its key) in the same transaction. A customer's bank connection, an already retired row, or an account still active in QuickBooks is refused (422). Median never reactivates the row; GET posting-setup reports quickbooks_account_inactive and quickbooks_account_reactivated instead.