refactor(billing): remove Stripe; payments are Payple (web) and Google Play (mobile)

Stripe is not used. Keeping its checkout, portal and webhook paths meant a
second payment provider, a second return-URL format and dead UI.

- Delete the stripe-checkout, stripe-portal and stripe-webhook functions and
  their config; billing-catalog serves Payple prices only, and the web parser
  rejects a catalog that still mixes in Stripe prices.
- Web: drop the Stripe checkout/portal buttons, provider toggle and return
  notices; billing shows Payple only. Past rows with provider='stripe' are
  still displayed ("Stripe (종료)") with a support contact instead of a portal.
- Desktop: delete the Stripe checkout modal, payment IPC channels, preload
  namespace and their types; "Remove ads with Pro" opens the web billing page
  via license.openBilling. Support/refund copy names Payple.
- billingUrl() loses the Stripe-only success/canceled result option; the
  Deno contract is regenerated.
- Migrations and the DB's accepted provider values are untouched (history).
- Docs and the backlog record the removal (MON-04, EXT-STRIPE-01, GAP-BILL-03).

Verified: typecheck (desktop/web/admin/api-client/mobile), contract:check,
deno check all functions, deno test 80/80, desktop 1478/1480 on the Electron
runtime (2 known environment failures), web and admin builds, release
metadata and mobile boundary self-tests, eslint on changed files.

apps/web/src/lib/billing-catalog.ts

@@ -1,6 +1,7 @@
 import type { SubscriptionTier } from '@d3ro/api-client'
 
-export type WebBillingProvider = 'payple' | 'stripe'
+/** 웹 결제사는 Payple(KRW) 하나다. Stripe는 2026-09-26 제거됐다. */
+export type WebBillingProvider = 'payple'
 export type BillingInterval = 'day' | 'week' | 'month' | 'year'
 
 export interface BillingCatalogPrice {
@@ -15,7 +16,7 @@ export interface BillingCatalog {
   plans: Record<'pro' | 'pro_plus', BillingCatalogPrice[]>
 }
 
-const PROVIDERS = new Set<WebBillingProvider>(['payple', 'stripe'])
+const PROVIDERS = new Set<WebBillingProvider>(['payple'])
 const INTERVALS = new Set<BillingInterval>(['day', 'week', 'month', 'year'])
 const PAID_TIERS = new Set(['pro', 'pro_plus'])
 
@@ -30,7 +31,7 @@ export function parseBillingCatalog(value: unknown): BillingCatalog | null {
     if (!rawPlan || typeof rawPlan !== 'object' || Array.isArray(rawPlan)) return null
     const plan = rawPlan as { tier?: unknown; prices?: unknown }
     if (typeof plan.tier !== 'string' || !PAID_TIERS.has(plan.tier) || seenTiers.has(plan.tier)) return null
-    if (!Array.isArray(plan.prices) || plan.prices.length > 2) return null
+    if (!Array.isArray(plan.prices) || plan.prices.length > PROVIDERS.size) return null
     seenTiers.add(plan.tier)
     const seenProviders = new Set<string>()
     for (const rawPrice of plan.prices) {
@@ -91,7 +92,5 @@ export function formatPlanCatalogPrice(
   if (tier === 'free') return '무료'
   if (!catalog) return null
   const prices = catalog.plans[tier]
-  if (prices.length === 0) return null
-  if (prices.length === 1) return formatBillingPrice(prices[0])
-  return prices.map((price) => `${price.provider === 'payple' ? 'Payple' : 'Stripe'} ${formatBillingPrice(price)}`).join(' · ')
+  return prices.length === 0 ? null : formatBillingPrice(prices[0])
 }

apps/web/src/lib/web-app-url.ts

@@ -1,15 +1,10 @@
 // apps/web/src/lib/web-app-url.ts
 // 웹앱 안에서 쓰는 절대 URL·복귀 경로 헬퍼. 주소 정본은 @d3ro/core/web-urls 다.
 //
-// 결제사(Stripe·Payple)와 OAuth 는 절대 URL 을 요구한다. 운영은 d3ro.chanpaca.net/app,
+// 결제사(Payple)와 OAuth 는 절대 URL 을 요구한다. 운영은 d3ro.chanpaca.net/app,
 // 로컬 개발은 localhost:3000/app 이므로 origin 만 현재 브라우저 것으로 바꿔 끼운다.
 
-import {
-  billingUrl,
-  PUBLIC_SITE_ORIGIN,
-  WEB_APP_BASE_PATH,
-  type BillingReturn
-} from '@d3ro/core/web-urls'
+import { billingUrl, PUBLIC_SITE_ORIGIN, WEB_APP_BASE_PATH } from '@d3ro/core/web-urls'
 
 /** 로그인 뒤 돌아갈 경로를 proxy 가 (app) 레이아웃에 넘길 때 쓰는 요청 헤더. */
 export const RETURN_PATH_HEADER = 'x-d3ro-return-path'
@@ -39,7 +34,7 @@ export function appUrlFor(origin: string, path: string): string {
 }
 
 /** 브라우저에서 결제 페이지 절대 URL. 쿼리 형식은 core billingUrl() 을 그대로 따른다. */
-export function browserBillingUrl(result?: BillingReturn): string {
-  const canonical = billingUrl(result ? { result } : {})
+export function browserBillingUrl(): string {
+  const canonical = billingUrl()
   return `${window.location.origin}${canonical.slice(PUBLIC_SITE_ORIGIN.length)}`
 }