feat: Subscriber portal web — login, dashboard, invoices, tickets (FIBEROPS-243-246)

- New route group app/(portal)/ separate from admin app
- Minimal portal layout with FiberOps branding, no admin nav
- portal-auth-store.ts: Zustand store with portal_token in localStorage
- portal-api.ts: Axios instance using portal_token + X-Tenant-Slug
- Login page: tenant slug + account number + password form
- Dashboard: account info, subscription details, balance due, quick links
- Invoices page: table with status badges (PAID/PARTIAL/OVERDUE/SENT)
- Tickets page: ticket list + New Ticket modal (POST /portal/tickets)
- Client detail profile tab: Portal Access Enabled/Disabled field
- portalAccessEnabled added to Client type

src/types/index.ts

@@ -52,6 +52,7 @@ export interface Client {
   updatedAt: string;
   area?: { id: string; name: string };
   subscriptions?: Subscription[];
+  portalAccessEnabled?: boolean;
 }
 
 export interface Subscription {