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/web/src/app/inicio/page.tsx

@@ -10,6 +10,7 @@ import {
   getPolicyStats,
   getPropertyStats,
   getStats,
+  listBankAccounts,
 } from "@/lib/api";
 import { useAuth } from "@/lib/abilities";
 import {
@@ -21,6 +22,7 @@ import {
   trustStatusLabel,
 } from "@/lib/labels";
 import type {
+  BankAccount,
   BankStats,
   BillingStats,
   CustomerStats,
@@ -41,7 +43,29 @@ interface DashboardData {
   policies: PolicyStats | null;
   properties: PropertyStats | null;
   billing: BillingStats | null;
+  /** Figures for ONE chequera — see `bankAccount` for which. */
   bank: BankStats | null;
+  /**
+   * The chequera the card above is reading. The office keeps more than one, in
+   * different currencies, so this card shows the default account rather than a
+   * cross-account total, which would be a figure that never existed.
+   */
+  bankAccount: BankAccount | null;
+  bankAccountCount: number;
+}
+
+/** Same default as /banco, so the two screens agree on which chequera opens. */
+function defaultAccount(accounts: BankAccount[]): BankAccount | null {
+  const remembered =
+    typeof window !== "undefined"
+      ? window.localStorage.getItem("banco.bankAccountId")
+      : null;
+  return (
+    accounts.find((a) => a.id === remembered) ??
+    accounts.find((a) => a.active) ??
+    accounts[0] ??
+    null
+  );
 }
 
 function HomeDashboard() {
@@ -52,25 +76,42 @@ function HomeDashboard() {
     properties: null,
     billing: null,
     bank: null,
+    bankAccount: null,
+    bankAccountCount: 0,
   });
   const [loading, setLoading] = useState(true);
 
   useEffect(() => {
     let alive = true;
+    // The chequera figures need an account id, so that read is a two-step:
+    // list the accounts, then ask the default one for its stats.
+    const bank = listBankAccounts().then(async (accounts) => {
+      const account = defaultAccount(accounts);
+      if (!account) return { account: null, stats: null, count: 0 };
+      return {
+        account,
+        stats: await getBankStats(account.id),
+        count: accounts.length,
+      };
+    });
+
     Promise.allSettled([
       getStats(),
       getPolicyStats(),
       getPropertyStats(),
       getBillingStats(),
-      getBankStats(),
+      bank,
     ]).then((results) => {
       if (!alive) return;
+      const bankResult = results[4].status === "fulfilled" ? results[4].value : null;
       setData({
         customers: results[0].status === "fulfilled" ? results[0].value : null,
         policies: results[1].status === "fulfilled" ? results[1].value : null,
         properties: results[2].status === "fulfilled" ? results[2].value : null,
         billing: results[3].status === "fulfilled" ? results[3].value : null,
-        bank: results[4].status === "fulfilled" ? results[4].value : null,
+        bank: bankResult?.stats ?? null,
+        bankAccount: bankResult?.account ?? null,
+        bankAccountCount: bankResult?.count ?? 0,
       });
       setLoading(false);
     });
@@ -260,22 +301,27 @@ function HomeDashboard() {
             loading={loading}
             title="Chequera del despacho"
             primary={
-              data.bank ? (
+              data.bank && data.bankAccount ? (
                 <span className={data.bank.net.startsWith("-") ? "money-neg" : "money-pos"}>
-                  {formatMoney(data.bank.net, "MXN")}
+                  {formatMoney(data.bank.net, data.bankAccount.currency)}
                 </span>
               ) : (
                 "—"
               )
             }
+            // Names the account, because this is one chequera's figure and the
+            // office has more than one — they are never added together.
             sub={
-              data.bank
-                ? balancePhrase(data.bank.net)
+              data.bank && data.bankAccount
+                ? `${data.bankAccount.label} · ${balancePhrase(data.bank.net)}`
                 : undefined
             }
             meta={
               data.bank
-                ? `${formatNumber(data.bank.movements)} movimientos · ${formatNumber(data.bank.pending)} pendientes`
+                ? `${formatNumber(data.bank.movements)} movimientos · ${formatNumber(data.bank.pending)} pendientes` +
+                  (data.bankAccountCount > 1
+                    ? ` · ${formatNumber(data.bankAccountCount)} cuentas en total`
+                    : "")
                 : undefined
             }
           />