feat(iap): native Myket in-app billing plugin (AIDL) + wire purchase/consume

Implements real Myket IAB for the Capacitor app (Myket has no purchase
deep-link like Bazaar — it uses the classic Google Play IAB v3 AIDL bound to
the Myket app):

- AIDL: com.android.vending.billing.IInAppBillingService (Myket-compatible).
- MyketBillingPlugin (Capacitor): binds ir.mservices.market via
  "ir.mservices.market.InAppBillingService.BIND", runs getBuyIntent →
  startIntentSenderForResult, verifies INAPP_DATA_SIGNATURE with the RSA key
  (Security.java, SHA1withRSA), returns the purchaseToken; consume() too.
- MainActivity registers the plugin + forwards the purchase activity result.
- Manifest: ir.mservices.market.BILLING permission + <queries> for Android 11+
  package visibility.
- build.gradle: enable buildFeatures.aidl (AGP 8 disables it by default).
- storeBilling: Myket goes through the plugin (RSA key embedded); after server
  verify, BuyCoins consumes the purchase so coins can be re-bought.

Bazaar (deep-link) and web (ZarinPal) paths unchanged. Needs on-device testing
with the Myket app installed + published products.

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

android/app/build.gradle

@@ -12,6 +12,10 @@ if (keystorePropsFile.exists()) {
 android {
     namespace = "com.bargevasat.app"
     compileSdk = rootProject.ext.compileSdkVersion
+    // AGP 8 disables AIDL by default; the Myket billing service needs it.
+    buildFeatures {
+        aidl true
+    }
     defaultConfig {
         applicationId "com.bargevasat.app"
         minSdkVersion rootProject.ext.minSdkVersion