feat(billing): Google Play build shows "not implemented" for coin buys

Add a gated `googleplay` store flavor (NEXT_PUBLIC_STORE=googleplay) so the
appeal/Play build ships a payment-free coin shop. isPurchaseDisabled() makes
BuyCoinsScreen short-circuit to a "not implemented" notice instead of starting
ZarinPal or Iranian IAB (both rejected on Play). Default web/Bazaar/Myket
builds are unaffected. New i18n key buy.notImplemented (fa+en).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/screens/BuyCoinsScreen.tsx

@@ -6,7 +6,7 @@ import { ScreenHeader, ScreenShell } from "@/components/online/ScreenHeader";
 import { useSessionStore } from "@/lib/session-store";
 import { useI18n } from "@/lib/i18n";
 import { getService } from "@/lib/online/service";
-import { consumeStorePurchase, isStoreBilling, purchaseViaStore } from "@/lib/storeBilling";
+import { consumeStorePurchase, isPurchaseDisabled, isStoreBilling, purchaseViaStore } from "@/lib/storeBilling";
 import { sound } from "@/lib/sound";
 import { CoinPack } from "@/lib/online/types";
 import { cn } from "@/lib/cn";
@@ -39,6 +39,14 @@ export function BuyCoinsScreen() {
     setBusy(p.id);
     setMsg("");
 
+    // Google Play build: coin purchases are intentionally not wired (no Iranian
+    // IAB on Play). Show a notice instead of starting any payment flow.
+    if (isPurchaseDisabled()) {
+      setMsg(t("buy.notImplemented"));
+      setBusy(null);
+      return;
+    }
+
     // Inside a store build (Cafe Bazaar / Myket), route through store billing.
     if (isStoreBilling()) {
       try {