feat(transactions): move an unbooked transaction to another cash account (#1570)

A bank transaction that ingested under the wrong cash account (or with no
account at all: legacy connections, own-account transfers the backfills
deliberately skipped) surfaces under the primary account's reconciliation
and can never be matched on the account it belongs to, because
cross-account matching is deliberately blocked. There was no first-party
way to fix the binding.

New PATCH /api/transactions/[id]/cash-account moves a movable staging row
(not booked, not invoice/supplier-invoice matched, not anchored via
transaction_voucher_links) to another of the company's cash accounts,
addressed by its BAS 19xx ledger account. Cross-currency moves are
hard-rejected (the row would vanish from every report's currency scope),
and the movable gate is re-asserted atomically in the UPDATE filter
against a concurrent book/auto-match, mirroring the title route. The tvl
check runs as a pre-check query since PostgREST cannot express NOT EXISTS
in an update filter; a tvl row appearing concurrently implies the booking
flow, which sets its own transaction state.

UI: 'Flytta till annat konto' in the transaction inbox row menu (opens a
radio-list dialog of the enabled cash accounts, current one preselected
and disabled) and direct 'Flytta till {name}' items in the bank
reconciliation unmatched-row menu that PATCH and refetch the view.

New structured error codes: TRANSACTION_MOVE_BOOKED,
TRANSACTION_MOVE_UNKNOWN_ACCOUNT, TRANSACTION_MOVE_CURRENCY_MISMATCH.

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

lib/api/schemas.ts

@@ -1480,6 +1480,18 @@ export const UpdateTransactionTitleSchema = z.object({
   description: z.string().trim().min(1, 'Title cannot be empty').max(500),
 })
 
+/**
+ * Move an unbooked bank transaction to another of the company's cash accounts,
+ * addressed by the target's BAS 19xx ledger account. Deliberately no null
+ * variant: unassigning a row would just re-strand it under the primary
+ * account's report (the exact symptom the move action exists to fix).
+ */
+export const MoveTransactionCashAccountSchema = z.object({
+  account_number: z
+    .string()
+    .regex(/^19\d{2}$/, 'Expected a BAS 19xx bank account number'),
+})
+
 export const BookInboxItemDirectlySchema = z.object({
   fiscal_period_id: uuid,
   entry_date: isoDate,