feat: aggregate portfolio data across accounts

Add authenticated all-account portfolio, operations, income and event endpoints. Preserve source accounts, exact currency totals and scoped cursor pagination.

src/tbank/account-reference.dto.ts

@@ -0,0 +1,10 @@
+import { ApiProperty } from '@nestjs/swagger';
+
+/** Source account of a row in an all-accounts response. */
+export class AccountReferenceDto {
+  @ApiProperty()
+  id: string;
+
+  @ApiProperty()
+  name: string;
+}