feat(auth): role-based permissions + user management (plan phase 1)

Adds the RBAC foundation the CRUD phases build on, and the first write
module (users). The platform was read-only: every controller was guarded
only by AuthenticatedGuard and UserRole was ADMIN|STAFF. The old PHP app
stored level+role but enforced neither, so this is a fresh design.

Permission model (server-authoritative):
- UserRole expanded to an ordered rank ADMIN > MANAGER > STAFF > VIEWER.
  VIEWER is the read-only role; STAFF+ can write.
- auth/abilities.ts: ROLE_RANK + ABILITY_MIN matrix + can()/abilitiesFor().
- @RequireAbility decorator + AbilityGuard enforce it on write routes;
  reads stay on AuthenticatedGuard so any logged-in user can read.
- /auth/login and /auth/me now return the resolved abilities map, so the
  web gates its UI off one payload instead of duplicating the rules.

User management (ADMIN-only, ability "user:manage"):
- UsersService gains list/create/update/resetPassword (argon2), never
  returns passwordHash; blocks self-deactivation and self-demotion;
  maps duplicate email to 409.
- UsersController: GET/POST /users, PATCH /users/:id,
  POST /users/:id/reset-password.
- Every mutation logged via new AuditService over the existing
  ActivityLog model (global CommonModule).

Web:
- AuthContext + useAuth/useCan; AppShell provides the user and gates the
  new "Usuarios" nav entry on user:manage; shows the user's role.
- /usuarios admin page: list + create/edit form + password reset +
  active toggle, Spanish-first, reusing existing card/table/field styles.

Schema pushed to dev (enum only, non-destructive). Verified end-to-end
against dev: admin CRUD works, VIEWER writes 403 while reads 200,
self-lockout guards and duplicate-email 409 all hold.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/api/src/common/audit.service.ts

@@ -0,0 +1,34 @@
+import { Injectable } from "@nestjs/common";
+import { Prisma } from "@jorgecuadros/database";
+import { PrismaService } from "../prisma/prisma.service";
+
+/**
+ * Thin writer over the existing ActivityLog model. Every mutating route calls
+ * this so who-did-what is recorded — the structural replacement for the old
+ * PHP app's scattered Logger calls. Best-effort: a logging failure must never
+ * fail the underlying write, so callers `void audit.log(...)` without awaiting.
+ */
+@Injectable()
+export class AuditService {
+  constructor(private readonly prisma: PrismaService) {}
+
+  async log(
+    userId: string | null | undefined,
+    event: string,
+    message?: Record<string, unknown>,
+    level = "info",
+  ): Promise<void> {
+    try {
+      await this.prisma.activityLog.create({
+        data: {
+          userId: userId ?? undefined,
+          event,
+          level,
+          message: (message as Prisma.InputJsonValue) ?? undefined,
+        },
+      });
+    } catch {
+      /* never let audit logging break a real write */
+    }
+  }
+}