feat(api): REST API with OpenAPI for other apps, behind Pireon OAuth

A REST adapter next to GraphQL (presenters/http) that calls the same
application services, so validation, permissions and domain errors are the
same: projects (members, board, stats, activity), issues (search, workflow,
assignee, release, links, comments, history), comments, releases and users.
Projects and issues can be addressed by id or key (WEB, WEB-12).

- Swagger UI at /api/docs, document at /api/docs-json and apps/api/openapi.json
  (rewritten by `nx serve api`, like schema.gql) for client generation.
- Every route but health/auth/webhook needs a Pireon token: the document
  declares Pireon OAuth2 (authorization code + PKCE, password) through the
  /api/auth/token proxy, and a bearer scheme for apps with their own client.
- configureApp() shares main.ts setup with the e2e, which now also covers REST.
- SWAGGER_ENABLED / OPENAPI_FILE config; docs 03/05 and library READMEs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/api/src/app/configure.ts

@@ -0,0 +1,13 @@
+import { INestApplication, ValidationPipe } from '@nestjs/common';
+import { DomainErrorFilter } from '@task-stream/api/shared/presenters';
+import { setupOpenApi } from './openapi';
+
+/** Everything main.ts sets on the app, shared with the e2e tests. */
+export function configureApp(app: INestApplication): void {
+  app.setGlobalPrefix('api');
+  app.enableCors();
+  app.enableShutdownHooks();
+  app.useGlobalPipes(new ValidationPipe({ transform: true, whitelist: true }));
+  app.useGlobalFilters(new DomainErrorFilter());
+  setupOpenApi(app);
+}