feat(portal-bff): admin user-directory read endpoint (#141)

## Summary

Second PR of the **portal-admin User-list chantier** per [ADR-0020](docs/decisions/0020-portal-admin-app.md) §"v1 scope — User list (read-only)". Ships the **read side**: paginated, filterable HTTP endpoint that queries the `public.users` directory populated at sign-in by PR #140. The SPA viewer screen lands in the final PR of the chantier.

## What lands

### [`AdminUsersQueryDto`](apps/portal-bff/src/admin/users-query.dto.ts)

Mirrors `AdminAuditQueryDto`'s posture — filters all optional, every unknown query key rejected by `forbidNonWhitelisted`, limit capped at **200** / default **50**.

| Filter | Type | Notes |
| --- | --- | --- |
| `username` | string ≤128 | Exact-prefix match (Prisma `startsWith`). |
| `displayName` | string ≤128 | Case-insensitive `contains` (display names vary in casing). |
| `audience` | enum | `workforce` \| `customer`. |
| `lastSeenAtFrom` | ISO-8601 | Inclusive lower bound. |
| `lastSeenAtTo` | ISO-8601 | Exclusive upper bound. |
| `limit` | int 1..200 | Default **50**. |
| `offset` | int ≥0 | Default **0**. |

### [`AdminUsersReader`](apps/portal-bff/src/admin/admin-users-reader.service.ts)

Prisma typed client against `public.users` — **no `SET LOCAL ROLE`** dance because `public.users` has no role-based privilege gate. The trust boundary is the controller's `@RequireAdmin` guard.

- **Order**: `last_seen_at DESC, oid ASC`. The second clause is a deterministic tie-breaker for pagination during sign-in bursts that share a timestamp.
- **COUNT + SELECT in one Prisma transaction** so the `total` reported to the SPA matches what's on the page even under a concurrent sign-in landing between the two queries.
- **Hard cap on limit** at 200 even when a caller bypasses the DTO — defense in depth on the BFF's event loop.

### [`AdminUsersController`](apps/portal-bff/src/admin/admin-users.controller.ts)

`GET /api/admin/users`, `@RequireAdmin()` at the class level. Forwards the validated DTO to `AdminUsersReader`, then emits `admin.users.query` with `{ filters, resultCount }` — the fishing-expedition deterrent (mirror of `admin.audit.query` from PR #132).

### [`AuditWriter.adminUsersQuery()`](apps/portal-bff/src/audit/audit.service.ts)

New typed method + `AdminUsersQueryInput` type. Same `outcome=success` / payload shape as `adminAuditQuery` — two distinct event types so a reviewer can pivot directly on `eventType` without parsing payload.

## Notes for the reviewer

- The shape mirrors `AdminAuditController` (#132) deliberately. Future admin read endpoints (CMS pages, menu items if they grow read filters) should adopt the same shape — keeps the SPA's data-flow pattern consistent across modules.
- `public.users` queries don't need `SET LOCAL ROLE` because there's no append-only / read-only role split on the table. That's a deliberate v1 simplification; if the security review later asks for stricter isolation we'd add a `users_reader` role + the same SET-LOCAL pattern AuditReader uses.
- The future "sign-in counts" join from `audit.events` on `actor_id_hash` is **deferred**. The salted hash is computable on the fly via `HashUserIdService`, so adding it later is a service-level change — no schema migration required.
- The `actor_id_hash` is deliberately **NOT** stored on `public.users` (per ADR-0013's invariant — the salt stays inside the audit module).

## Test plan

- [x] `pnpm nx test portal-bff` — **391 specs pass** (was 365; +26 covering DTO validation, reader transaction shape + filter forwarding + pagination defaults + cap, controller path, audit typed method).
- [x] `pnpm exec nx affected -t format:check lint test build --base=origin/main` — clean.
- [x] Prisma transaction shape verified: COUNT + SELECT both fire exactly once per call; tuple-return contract honoured.
- [x] Filter projections verified per filter: username `startsWith`, displayName case-insensitive `contains`, audience exact match, lastSeenAt `gte/lt` composition.
- [ ] e2e — pending the admin SPA viewer screen + a real admin session. Once both exist: `curl --cookie 'portal_admin_session=...' /api/admin/users?username=jane&limit=10` returns the matching subset and a new `admin.users.query` audit row lands.

## What's next

The chantier's final PR:

- **portal-admin `/users` screen** — SPA viewer with filter form + table + pagination. Same shape as the `/audit` page (PR #136): signal-driven state, color-coded badges for audience, ISO timestamps formatted locale-side, status states. Will graduate the sidebar entry from `aria-disabled` "Soon" badge to a live link.

---------

Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #141

apps/portal-bff/src/admin/admin-users-reader.service.spec.ts

@@ -0,0 +1,147 @@
+import { Test } from '@nestjs/testing';
+import { PrismaService } from 'nestjs-prisma';
+import { AdminUsersReader } from './admin-users-reader.service';
+
+interface MockPrisma {
+  user: {
+    count: jest.Mock;
+    findMany: jest.Mock;
+  };
+  $transaction: jest.Mock;
+}
+
+function buildPrisma(opts?: { count?: number; items?: unknown[] }): MockPrisma {
+  const count = jest.fn().mockResolvedValue(opts?.count ?? 0);
+  const findMany = jest.fn().mockResolvedValue(opts?.items ?? []);
+  return {
+    user: { count, findMany },
+    // The reader calls $transaction with the promises returned by
+    // `count()` + `findMany()` — the operations have already fired
+    // by the time $transaction sees them. The mock just resolves
+    // them together so Prisma's tuple-return contract is honoured.
+    $transaction: jest
+      .fn()
+      .mockImplementation((promises: ReadonlyArray<Promise<unknown>>) => Promise.all(promises)),
+  };
+}
+
+async function createSubject(prisma: MockPrisma): Promise<AdminUsersReader> {
+  const moduleRef = await Test.createTestingModule({
+    providers: [AdminUsersReader, { provide: PrismaService, useValue: prisma }],
+  }).compile();
+  return moduleRef.get(AdminUsersReader);
+}
+
+const ROW = {
+  oid: 'user-oid',
+  tid: 'tenant-1',
+  audience: 'workforce',
+  username: 'jane.doe@apf.example',
+  displayName: 'Jane Doe',
+  firstSeenAt: new Date('2026-05-10T10:00:00.000Z'),
+  lastSeenAt: new Date('2026-05-14T08:30:00.000Z'),
+};
+
+describe('AdminUsersReader.findUsers', () => {
+  it('issues a COUNT + SELECT in a single Prisma transaction', async () => {
+    const prisma = buildPrisma({ count: 5, items: [ROW] });
+    const reader = await createSubject(prisma);
+    const page = await reader.findUsers({});
+    expect(prisma.$transaction).toHaveBeenCalledTimes(1);
+    expect(prisma.user.count).toHaveBeenCalledTimes(1);
+    expect(prisma.user.findMany).toHaveBeenCalledTimes(1);
+    expect(page.total).toBe(5);
+    expect(page.items).toHaveLength(1);
+  });
+
+  it('projects rows into the SPA-facing shape (ISO timestamps)', async () => {
+    const prisma = buildPrisma({ items: [ROW] });
+    const reader = await createSubject(prisma);
+    const page = await reader.findUsers({});
+    expect(page.items[0]).toEqual({
+      oid: 'user-oid',
+      tid: 'tenant-1',
+      audience: 'workforce',
+      username: 'jane.doe@apf.example',
+      displayName: 'Jane Doe',
+      firstSeenAt: '2026-05-10T10:00:00.000Z',
+      lastSeenAt: '2026-05-14T08:30:00.000Z',
+    });
+  });
+
+  it('orders by last_seen_at DESC, oid ASC for deterministic pagination', async () => {
+    const prisma = buildPrisma();
+    const reader = await createSubject(prisma);
+    await reader.findUsers({});
+    const findManyArgs = prisma.user.findMany.mock.calls[0]?.[0] as {
+      orderBy: ReadonlyArray<Record<string, string>>;
+    };
+    expect(findManyArgs.orderBy).toEqual([{ lastSeenAt: 'desc' }, { oid: 'asc' }]);
+  });
+
+  it('passes startsWith filter on username through to Prisma', async () => {
+    const prisma = buildPrisma();
+    const reader = await createSubject(prisma);
+    await reader.findUsers({ username: 'jane' });
+    const args = prisma.user.findMany.mock.calls[0]?.[0] as {
+      where: { username?: { startsWith?: string } };
+    };
+    expect(args.where.username).toEqual({ startsWith: 'jane' });
+  });
+
+  it('passes case-insensitive contains filter on displayName through to Prisma', async () => {
+    const prisma = buildPrisma();
+    const reader = await createSubject(prisma);
+    await reader.findUsers({ displayName: 'doe' });
+    const args = prisma.user.findMany.mock.calls[0]?.[0] as {
+      where: { displayName?: { contains?: string; mode?: string } };
+    };
+    expect(args.where.displayName).toEqual({ contains: 'doe', mode: 'insensitive' });
+  });
+
+  it('combines lastSeenAtFrom and lastSeenAtTo into a single gte/lt range filter', async () => {
+    const prisma = buildPrisma();
+    const reader = await createSubject(prisma);
+    await reader.findUsers({
+      lastSeenAtFrom: '2026-05-01T00:00:00.000Z',
+      lastSeenAtTo: '2026-05-14T23:59:59.999Z',
+    });
+    const args = prisma.user.findMany.mock.calls[0]?.[0] as {
+      where: { lastSeenAt?: { gte?: Date; lt?: Date } };
+    };
+    expect(args.where.lastSeenAt?.gte).toBeInstanceOf(Date);
+    expect(args.where.lastSeenAt?.lt).toBeInstanceOf(Date);
+    expect(args.where.lastSeenAt?.gte?.toISOString()).toBe('2026-05-01T00:00:00.000Z');
+    expect(args.where.lastSeenAt?.lt?.toISOString()).toBe('2026-05-14T23:59:59.999Z');
+  });
+
+  it('applies default limit (50) and offset (0) when not provided', async () => {
+    const prisma = buildPrisma();
+    const reader = await createSubject(prisma);
+    const page = await reader.findUsers({});
+    const args = prisma.user.findMany.mock.calls[0]?.[0] as {
+      take: number;
+      skip: number;
+    };
+    expect(args.take).toBe(50);
+    expect(args.skip).toBe(0);
+    expect(page.limit).toBe(50);
+    expect(page.offset).toBe(0);
+  });
+
+  it('caps limit at MAX_LIMIT (200) even when a caller bypasses the DTO', async () => {
+    const prisma = buildPrisma();
+    const reader = await createSubject(prisma);
+    await reader.findUsers({ limit: 1000 });
+    const args = prisma.user.findMany.mock.calls[0]?.[0] as { take: number };
+    expect(args.take).toBe(200);
+  });
+
+  it('emits no WHERE clause when no filter is provided', async () => {
+    const prisma = buildPrisma();
+    const reader = await createSubject(prisma);
+    await reader.findUsers({});
+    const args = prisma.user.findMany.mock.calls[0]?.[0] as { where: object };
+    expect(args.where).toEqual({});
+  });
+});