feat(bank): multi-bank chequera — required bankAccountId, per-account scoping

The office keeps more than one operating account (Utilities banks in MXN,
Seguros in USD), but bank_transactions was a single implicit MXN register by
design. Adds Bank/BankAccount and makes every read and write in the module
scoped to exactly one account.

Schema:
- Bank / BankAccount. Currency is fixed per account and BankTransaction has
  no currency column of its own — a movement inherits its account's, the way
  a real bank account doesn't mix currencies.
- BankTransaction.bankAccountId, required. A movement with no known account
  isn't reconcilable against a statement.
- @@index([bankAccountId, transactionDate]): every read now filters by
  account and orders/groups by date.

Migration:
- backfill_bank_accounts.py seeds Scotiabank + "Utilities — Scotiabank (MXN)"
  and backfills all 22,669 existing rows onto it, then promotes the column to
  NOT NULL and attaches the FK. Standalone because prisma db push cannot add
  a required column to a populated table. Idempotent; re-running once a second
  account exists does not re-point rows.
- run_all.py runs it (both modes) before transform_bank.py, which now resolves
  the account by label and fails fast if it is missing.

API:
- ?bankAccountId= required on list/stats/facets/summary — not optional with an
  "all accounts" default, since summing an MXN and a USD register repeats the
  currency-collapsing mistake the billing module exists to prevent. Missing is
  400, unknown is 404.
- facets() had no account clause at all and summary() has two raw-SQL rollups;
  all three are now parameterised. Scoping only one of summary's queries would
  leave the year list and its drill-down describing different books.
- New bank/accounts + bank/banks sub-resource under a MANAGER
  bank:manage-accounts ability. currency is absent from the update DTO: booked
  movements are denominated in it, so editing would re-denominate history.
  Capture into a closed account is rejected.

Web:
- /banco gains an account picker (remembered per browser) and reads every
  figure in the selected account's currency; the "single currency (MXN)"
  doc-comment and the hardcoded MXN formatting are gone.
- New /banco/cuentas for banks and accounts. Accounts are closed, never
  deleted — the FK is required, so deleting one would destroy its register.
- /inicio's chequera card names the account it is reading instead of implying
  a single register.

Verified against dev + browser: a second USD account showed full read/write
isolation from the MXN register, whose totals were unchanged (22,669
movements, net 1,014,266.97).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/api/src/auth/abilities.ts

@@ -31,6 +31,7 @@ export type Ability =
   | "ledger:void"
   | "bank:create"
   | "bank:void"
+  | "bank:manage-accounts"
   | "lookup:manage"
   | "user:manage"
   | "db:manage";
@@ -50,6 +51,9 @@ export const ABILITY_MIN: Record<Ability, Role> = {
   "ledger:void": "MANAGER",
   "bank:create": "STAFF",
   "bank:void": "MANAGER",
+  // Opening or renaming a chequera is rarer and higher-stakes than posting a
+  // movement into one — a wrong account silently mixes two sets of books.
+  "bank:manage-accounts": "MANAGER",
   "lookup:manage": "MANAGER",
   "user:manage": "ADMIN",
   "db:manage": "ADMIN",