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

lib/portal-auth-store.ts

@@ -0,0 +1,53 @@
+import { create } from 'zustand';
+import { persist } from 'zustand/middleware';
+import portalApi from './portal-api';
+
+interface PortalSubscriber {
+  accountNumber: string;
+  firstName: string;
+  lastName: string;
+}
+
+interface PortalAuthState {
+  subscriber: PortalSubscriber | null;
+  portalToken: string | null;
+  tenantSlug: string | null;
+  isAuthenticated: boolean;
+  login: (tenantSlug: string, accountNumber: string, password: string) => Promise<void>;
+  logout: () => void;
+}
+
+export const usePortalAuthStore = create<PortalAuthState>()(
+  persist(
+    (set) => ({
+      subscriber: null,
+      portalToken: null,
+      tenantSlug: null,
+      isAuthenticated: false,
+      login: async (tenantSlug, accountNumber, password) => {
+        const res = await portalApi.post('/api/v1/portal/auth/login', {
+          tenantSlug,
+          accountNumber,
+          password,
+        });
+        const { token, subscriber } = res.data;
+        localStorage.setItem('portal_token', token);
+        set({
+          portalToken: token,
+          tenantSlug,
+          subscriber: {
+            accountNumber: subscriber.accountNumber,
+            firstName: subscriber.firstName,
+            lastName: subscriber.lastName,
+          },
+          isAuthenticated: true,
+        });
+      },
+      logout: () => {
+        localStorage.removeItem('portal_token');
+        set({ subscriber: null, portalToken: null, tenantSlug: null, isAuthenticated: false });
+      },
+    }),
+    { name: 'portal_auth' }
+  )
+);