feat(billing): update frontend for polar migration

Update billing types, remove invoice preview, replace Stripe invoice
display with Polar orders, update tax ID from array to single object,
remove upcoming invoice amount display.

lib/api/admin.ts

@@ -2,8 +2,8 @@ import { authFetch } from './client'
 
 export interface AdminOrgSummary {
   organization_id: string
-  stripe_customer_id: string
-  stripe_subscription_id: string
+  billing_customer_id: string
+  billing_subscription_id: string
   plan_id: string
   billing_interval: string
   pageview_limit: number

lib/api/billing.ts

@@ -19,16 +19,10 @@ export interface SubscriptionDetails {
   sites_count?: number
   /** Pageviews in current billing period (when pageview_limit > 0). Present when backend supports usage API. */
   pageview_usage?: number
-  /** Business name from Stripe Tax ID collection / business purchase flow (optional). */
+  /** Business name from billing (optional). */
   business_name?: string
-  /** Tax IDs collected on the Stripe customer (VAT, EIN, etc.) for invoice verification. */
-  tax_ids?: TaxID[]
-  /** Next invoice amount in cents (for "Renews on X for €Y" display). */
-  next_invoice_amount_due?: number
-  /** Currency for next invoice (e.g. eur). */
-  next_invoice_currency?: string
-  /** Unix timestamp when next invoice period ends. */
-  next_invoice_period_end?: number
+  /** Tax ID collected on the billing customer (VAT, EIN, etc.). */
+  tax_id?: TaxID | null
 }
 
 export async function getSubscription(): Promise<SubscriptionDetails> {
@@ -66,22 +60,6 @@ export interface ChangePlanParams {
   limit: number
 }
 
-export interface PreviewInvoiceResult {
-  amount_due: number
-  currency: string
-  period_end: number
-}
-
-export async function previewInvoice(params: ChangePlanParams): Promise<PreviewInvoiceResult | null> {
-  const res = await apiRequest<PreviewInvoiceResult | Record<string, never>>('/api/billing/preview-invoice', {
-    method: 'POST',
-    body: JSON.stringify(params),
-  })
-  if (res && typeof res === 'object' && 'amount_due' in res && typeof (res as PreviewInvoiceResult).amount_due === 'number') {
-    return res as PreviewInvoiceResult
-  }
-  return null
-}
 
 export async function changePlan(params: ChangePlanParams): Promise<{ ok: boolean }> {
   return apiRequest<{ ok: boolean }>('/api/billing/change-plan', {
@@ -103,17 +81,18 @@ export async function createCheckoutSession(params: CreateCheckoutParams): Promi
   })
 }
 
-export interface Invoice {
+export interface Order {
   id: string
-  amount_paid: number
-  amount_due: number
+  total_amount: number
+  subtotal_amount: number
+  tax_amount: number
   currency: string
   status: string
-  created: number
-  hosted_invoice_url: string
-  invoice_pdf: string
+  created_at: string
+  paid: boolean
+  invoice_number: string
 }
 
-export async function getInvoices(): Promise<Invoice[]> {
-  return apiRequest<Invoice[]>('/api/billing/invoices')
+export async function getOrders(): Promise<Order[]> {
+  return apiRequest<Order[]>('/api/billing/invoices')
 }