refactor: organize backend by business responsibility

src/modules/investments/portfolio/portfolio.api.ts

@@ -0,0 +1,7 @@
+// Public cross-module surface. Nest providers are exported by the matching module.
+export { totalsByCurrency } from './infrastructure/tbank-portfolio.mapper';
+export {
+  PortfolioDto,
+  PortfolioPositionDto,
+} from './presentation/portfolio.dto';
+export { PortfolioService } from './application/portfolio.service';