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/billing-catalog/index.ts

@@ -2,8 +2,6 @@ import { corsHeaders, handleCorsPreflightRequest } from '../_shared/cors.ts'
 import { requireUser, authErrorResponse, type AuthError } from '../_shared/auth.ts'
 import {
   createBillingCatalog,
-  parseStripeCatalogPrice,
-  type BillingCatalogPrice,
   type BillingCatalogTier,
 } from '../_shared/billing-catalog.ts'
 import {
@@ -23,20 +21,6 @@ function jsonResponse(body: unknown, status = 200): Response {
   return new Response(JSON.stringify(body), { status, headers: NO_STORE_HEADERS })
 }
 
-async function loadStripePrice(
-  secretKey: string,
-  priceId: string,
-): Promise<Omit<BillingCatalogPrice, 'provider'> | null> {
-  const response = await fetch(`https://api.stripe.com/v1/prices/${encodeURIComponent(priceId)}`, {
-    method: 'GET',
-    headers: { Authorization: `Bearer ${secretKey}` },
-    signal: AbortSignal.timeout(8_000),
-  })
-  if (!response.ok) return null
-  const payload = await response.json().catch(() => null)
-  return parseStripeCatalogPrice(payload, priceId)
-}
-
 Deno.serve(async (req: Request) => {
   const preflight = handleCorsPreflightRequest(req)
   if (preflight) return preflight
@@ -56,24 +40,7 @@ Deno.serve(async (req: Request) => {
       if (!(error instanceof PaypleConfigurationError)) throw error
     }
 
-    const stripeSecret = Deno.env.get('STRIPE_SECRET_KEY')?.trim() ?? ''
-    const stripeIds: Record<BillingCatalogTier, string> = {
-      pro: Deno.env.get('STRIPE_PRICE_PRO')?.trim() ?? '',
-      pro_plus: (Deno.env.get('STRIPE_PRICE_PRO_PLUS')
-        ?? Deno.env.get('STRIPE_PRICE_TEAM'))?.trim() ?? '',
-    }
-    const stripe: Partial<Record<BillingCatalogTier, Omit<BillingCatalogPrice, 'provider'>>> = {}
-    if (stripeSecret) {
-      const tiers: BillingCatalogTier[] = ['pro', 'pro_plus']
-      await Promise.all(tiers.map(async (tier) => {
-        const priceId = stripeIds[tier]
-        if (!priceId) return
-        const price = await loadStripePrice(stripeSecret, priceId).catch(() => null)
-        if (price) stripe[tier] = price
-      }))
-    }
-
-    return jsonResponse(createBillingCatalog({ payple, stripe }))
+    return jsonResponse(createBillingCatalog({ payple }))
   } catch (error) {
     if (error && typeof error === 'object' && 'status' in error && 'message' in error) {
       return authErrorResponse(error as AuthError, NO_STORE_HEADERS)