docs: v3.1 gap analysis + delivery plan; add DI seams to 9 admin gateways

Adds InjectionToken + factory for Orders, Products, Users, Transactions,
Monitoring, Moderation (mirrors existing Categories/Dashboard pattern) and
repoints their facades plus the derived Analytics/Customers facades and
admin-order-watcher off the mock LocalGateway class directly. No behavior
change today - still resolves to the mock - but a real backend can now be
bound per domain with zero facade edits.

Docs: full gap analysis of Product Plan v3.1 against current repo state,
and a phased delivery plan (10 phases, 34 sprints, 5 tracks) breaking every
identified gap into scoped, sequenced work.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/features/admin/users/services/admin-users-gateway.token.ts

@@ -0,0 +1,9 @@
+import { InjectionToken, inject } from '@angular/core';
+import { AdminUsersGateway } from './admin-users-gateway.interface';
+import { AdminUsersLocalGateway } from './admin-users-local.gateway';
+
+/** Swap point for a real Users backend - see BACKEND-API-REFERENCE.md §8 (no seam existed before this token). */
+export const ADMIN_USERS_GATEWAY = new InjectionToken<AdminUsersGateway>('ADMIN_USERS_GATEWAY', {
+  providedIn: 'root',
+  factory: () => inject(AdminUsersLocalGateway),
+});