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

app/(app)/clients/[id]/page.tsx

@@ -547,6 +547,15 @@ export default function ClientDetailPage() {
                   <dd className="mt-0.5 text-sm text-gray-900">{value}</dd>
                 </div>
               ))}
+              <div>
+                <dt className="text-xs font-medium text-gray-400 uppercase tracking-wide">Portal Access</dt>
+                <dd className="mt-0.5 text-sm">
+                  {client.portalAccessEnabled
+                    ? <span className="text-green-600 font-medium">Enabled</span>
+                    : <span className="text-gray-400">Disabled</span>
+                  }
+                </dd>
+              </div>
             </dl>
           </CardContent>
         </Card>