feat(portal-bff): openapi spec + scalar api reference UI (dev-only) (#143)

## Summary

Adds an OpenAPI 3 spec + a [Scalar API Reference](https://scalar.com/) UI to `portal-bff`, dev-only. The BFF previously had no way to *see* its HTTP surface short of grepping for `@Get` / `@Post`; this PR generates the spec from the existing Nest controllers via [`@nestjs/swagger`](https://docs.nestjs.com/openapi/introduction) and renders it through Scalar — a modern alternative to the classic Swagger UI (single-page, fast, dark-mode native, better typography).

## What lands

### Two new dev-only routes

| Route | What it serves |
| --- | --- |
| `GET /api/openapi.json` | Raw OpenAPI 3 document. External tools (Bruno / Insomnia / Postman) import from here. |
| `GET /api/docs` | Scalar API Reference HTML page. Loads the JSON spec at render time and renders the full endpoint catalogue with a "Try it" panel. |

Both routes are gated behind `process.env.NODE_ENV !== 'production'` in [`setupOpenApi`](apps/portal-bff/src/openapi/openapi.ts) — production deployments don't need the docs surface, and publishing it would hand an attacker a curated map of every authenticated endpoint + every DTO shape. If a future ops use-case wants the spec in prod (internal gateway, contract testing), the gate is one line away from an opt-in `OPENAPI_PUBLISH=true` env knob.

### Core implementation — [`apps/portal-bff/src/openapi/openapi.ts`](apps/portal-bff/src/openapi/openapi.ts)

Two exported helpers:

- **`buildOpenApiDocument(app)`** — wraps Nest's `DocumentBuilder` + `SwaggerModule.createDocument`. Sets title, description (mentions the CSRF caveat — see below), version, and registers **two** cookie security schemes:
  - `portal_session` for the user-portal surface ([ADR-0009](docs/decisions/0009-auth-flow-oidc-pkce-msal-node.md)).
  - `portal_admin_session` for the admin-portal surface ([ADR-0020](docs/decisions/0020-portal-admin-app.md)).
  No `@ApiBearerAuth` is declared — the BFF never exposes a bearer-auth surface (SPA never holds tokens per ADR-0009; downstream OBO tokens are server-side only per ADR-0014).

- **`setupOpenApi(app, globalPrefix)`** — short-circuits in production, otherwise binds the two routes via the Express adapter directly (`app.getHttpAdapter().get(...)` and `app.use(...)`). The OpenAPI JSON is a static asset and Scalar is a vanilla Express middleware — wrapping either in a Nest controller would add zero value and an extra layer of indirection.

Wired into bootstrap at [`apps/portal-bff/src/main.ts:220`](apps/portal-bff/src/main.ts#L220), immediately after the JWKS endpoint mount and before `app.listen()`.

### Controllers decorated with `@ApiTags` / `@ApiOperation` / `@ApiCookieAuth`

Annotations are cosmetic but make the spec actually browsable. Tag taxonomy:

| Controller | Tag | Security |
| --- | --- | --- |
| [`AppController`](apps/portal-bff/src/app/app.controller.ts) | `app (scaffolding)` | — |
| [`HealthController`](apps/portal-bff/src/health/health.controller.ts) | `health` | — |
| [`AuthController`](apps/portal-bff/src/auth/auth.controller.ts) | `auth (user portal)` | `portal_session` on `/me` + `/logout` |
| [`AdminAuthController`](apps/portal-bff/src/admin/admin-auth.controller.ts) | `auth (admin portal)` | `portal_admin_session` on `/me` + `/logout` |
| [`AdminController`](apps/portal-bff/src/admin/admin.controller.ts) | `admin (self-test)` | class-level `portal_admin_session` |
| [`AdminAuditController`](apps/portal-bff/src/admin/admin-audit.controller.ts) | `admin (audit log)` | class-level `portal_admin_session` |
| [`AdminUsersController`](apps/portal-bff/src/admin/admin-users.controller.ts) | `admin (user directory)` | class-level `portal_admin_session` |

`@ApiOperation({ summary: … })` added on every route — populates the one-line description Scalar shows in its left-rail TOC.

### Deps + Jest

- `@nestjs/swagger ^11` (matches the Nest 11 major already pinned) and `@scalar/nestjs-api-reference` added to the workspace root.
- [`jest.config.cts`](apps/portal-bff/jest.config.cts) — widened `transformIgnorePatterns` from `/node_modules/(?!.*jose)/` to `/node_modules/(?!.*(jose|@scalar/))/`. `@scalar/client-side-rendering` (a transitive dep) ships ESM-only; without this widening the spec suite fails to load the module under ts-jest.

## Notes for the reviewer

- **Why two cookie schemes rather than one?** Scalar renders a per-endpoint lock icon driven by the security scheme name. Splitting `portal_session` / `portal_admin_session` keeps the indicator semantically truthful — `/api/auth/me` and `/api/admin/auth/me` look identical otherwise.
- **CSRF caveat.** Mutating routes (`POST` / `PUT` / `PATCH` / `DELETE`) require `X-CSRF-Token` per [ADR-0009](docs/decisions/0009-auth-flow-oidc-pkce-msal-node.md). The header must be set manually in Scalar's "Try it" panel to the value of the `portal_csrf` cookie when exercising those routes. The spec description mentions it; auto-injecting the header from the cookie is a future polish.
- **No ADR for this.** `@nestjs/swagger` is the framework's own first-party tooling; Scalar is a thin UI on top of a standard OpenAPI 3 document. Both replaceable without touching the controllers (the `@Api*` annotations are spec-standard). Dev-only, no prod surface — doesn't cross any of the bars that warrant an ADR per [CLAUDE.md](CLAUDE.md).
- **Express-layer routing.** Same pattern as the JWKS endpoint (#139): the OpenAPI JSON is a static asset and Scalar a vanilla Express handler, so wiring through Nest's router adds no value.

## Test plan

- [x] **5 new specs** in [`apps/portal-bff/src/openapi/openapi.spec.ts`](apps/portal-bff/src/openapi/openapi.spec.ts) — document shape (openapi version, title, version), both cookie schemes declared, smoke controller route captured in `paths`, production short-circuit (no routes mounted, no `app.use` called), dev mount (JSON at `/api/openapi.json` via the HTTP adapter, Scalar UI at `/api/docs` via `app.use`).
- [x] `pnpm nx test portal-bff` — **396 specs pass** (was 391).
- [x] `pnpm exec nx affected -t format:check lint test build --base=origin/main` — clean.
- [x] Manual dev smoke: `pnpm nx serve portal-bff`, `curl /api/openapi.json | jq .info` returns title + version, open `/api/docs` in a browser, every controller's routes visible under their tag, lock icons match the cookie scheme on guarded routes.

## What's next — light follow-ups

Not blocking this PR; mentioned so they're not lost:

- Auto-inject the `X-CSRF-Token` header in Scalar from the `portal_csrf` cookie (custom Scalar config preset).
- Promote `@ApiOperation` summaries with multi-line `description`s on the more involved routes (`/api/admin/audit`, `/api/admin/users`).
- Annotate DTOs with `@ApiProperty` once the first contract-test consumer arrives — Nest can also pick them up automatically with the `@nestjs/swagger` ts-plugin if we wire it into the Nx build target. Deferred until the spec is consumed by tooling that benefits from the precision.

---------

Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #143

apps/portal-bff/src/app/app.controller.ts

@@ -1,6 +1,8 @@
 import { Controller, Get } from '@nestjs/common';
+import { ApiTags } from '@nestjs/swagger';
 import { AppService } from './app.service';
 
+@ApiTags('app (scaffolding)')
 @Controller()
 export class AppController {
   constructor(private readonly appService: AppService) {}