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.

server/supabase/functions/_shared/billing-catalog.test.ts

@@ -1,65 +1,33 @@
-import {
-  createBillingCatalog,
-  parseStripeCatalogPrice,
-} from './billing-catalog.ts'
+import { createBillingCatalog } from './billing-catalog.ts'
 import { PLAN_PRICE_KRW } from './core-contract.generated.ts'
 
 function assert(condition: unknown, message: string): asserts condition {
   if (!condition) throw new Error(message)
 }
 
-Deno.test('Stripe catalog accepts only the exact active recurring price', () => {
-  const parsed = parseStripeCatalogPrice({
-    id: 'price_pro',
-    active: true,
-    type: 'recurring',
-    unit_amount: 990,
-    currency: 'usd',
-    recurring: { interval: 'month', interval_count: 1 },
-  }, 'price_pro')
-  assert(parsed?.unit_amount === 990, 'amount must be preserved')
-  assert(parsed?.currency === 'USD', 'currency must be normalized')
-  assert(parsed?.interval === 'month', 'interval must be preserved')
-})
-
-Deno.test('Stripe catalog rejects mismatched, inactive, free, malformed, and one-time prices', () => {
-  const base = {
-    id: 'price_pro',
-    active: true,
-    type: 'recurring',
-    unit_amount: 990,
-    currency: 'usd',
-    recurring: { interval: 'month', interval_count: 1 },
-  }
-  const invalid = [
-    { ...base, id: 'price_other' },
-    { ...base, active: false },
-    { ...base, type: 'one_time', recurring: null },
-    { ...base, unit_amount: 0 },
-    { ...base, currency: 'US$' },
-    { ...base, recurring: { interval: 'minute', interval_count: 1 } },
-    { ...base, recurring: { interval: 'month', interval_count: 0 } },
-  ]
-  for (const value of invalid) {
-    assert(parseStripeCatalogPrice(value, 'price_pro') === null, 'invalid Stripe price must fail closed')
-  }
-})
-
-Deno.test('catalog exposes only configured provider prices and never invents a fallback', () => {
+Deno.test('catalog exposes only configured Payple prices and never invents a fallback', () => {
   const catalog = createBillingCatalog({
     payple: { pro: PLAN_PRICE_KRW.pro, pro_plus: PLAN_PRICE_KRW.pro_plus },
-    stripe: {
-      pro: { unit_amount: 990, currency: 'USD', interval: 'month', interval_count: 1 },
-    },
   })
-  assert(catalog.plans[0].prices.length === 2, 'pro must expose two verified providers')
-  assert(catalog.plans[1].prices.length === 1, 'pro plus must omit unavailable Stripe')
+  assert(
+    catalog.plans.every((plan) => plan.prices.length === 1 && plan.prices[0].provider === 'payple'),
+    'each paid plan must expose exactly one Payple price',
+  )
   assert(
     catalog.plans[0].prices[0].unit_amount === PLAN_PRICE_KRW.pro
       && catalog.plans[1].prices[0].unit_amount === PLAN_PRICE_KRW.pro_plus,
     'Payple prices must come from the core plan catalog',
   )
+  assert(
+    catalog.plans.every((plan) => plan.prices[0].currency === 'KRW' && plan.prices[0].interval === 'month'),
+    'Payple prices are monthly KRW',
+  )
 
   const unavailable = createBillingCatalog({})
   assert(unavailable.plans.every((plan) => plan.prices.length === 0), 'missing configuration must stay unavailable')
 })
+
+Deno.test('catalog rejects non-positive or non-integer Payple amounts', () => {
+  const catalog = createBillingCatalog({ payple: { pro: 0, pro_plus: 1.5 } })
+  assert(catalog.plans.every((plan) => plan.prices.length === 0), 'invalid amounts must fail closed')
+})