fix(prod): payment/tax gateways never fake success outside Development

Production-readiness audit fixes — every mock fallback is now gated on
IsDevelopment; in production these paths fail loudly instead:

- ZarinPal/Tara/SnappPay init: missing credentials returned a MOCK
  payment URL whose callback verified as paid — a café could activate a
  paid plan without paying. Now: "Payment gateway is not configured."
- Tara/SnappPay verify: a forged MOCK-* trace/token on the callback was
  accepted as a verified payment in any environment. Now rejected
  outside Development.
- Taraz (سامانه مودیان): returned a fake MOCK-TARAZ tracking code as if
  invoices reached the tax authority. Now returns an honest error (the
  real integration is not built yet).
- Admin integrations: NextPay/Vandar removed — they were listed but have
  no gateway implementation (selecting them silently used ZarinPal).
- docker-compose: ASPNETCORE_ENVIRONMENT default flipped Development →
  Production so a missing env var can never run prod in dev mode.

86 tests pass.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/Meezi.Admin.API/Services/PlatformIntegrationService.cs

@@ -22,13 +22,14 @@ public class PlatformIntegrationService : IPlatformIntegrationService
     public const string KeyKavenegarEnabled      = "integrations.kavenegar.enabled";
     public const string KeyKavenegarSender       = "integrations.kavenegar.senderNumber";
 
+    // Only gateways the BillingPaymentOrchestrator actually implements. NextPay
+    // and Vandar were listed here before they had any implementation — enabling
+    // them silently fell back to ZarinPal, which is a trap for the operator.
     private static readonly (string Id, string NameFa, string Prefix)[] Gateways =
     [
         ("zarinpal", "زرین‌پال", "payment.zarinpal"),
         ("tara", "تارا", "payment.tara"),
-        ("snapppay", "اسنپ‌پی", "payment.snapppay"),
-        ("nextpay", "نکست‌پی", "payment.nextpay"),
-        ("vandar", "وندار", "payment.vandar")
+        ("snapppay", "اسنپ‌پی", "payment.snapppay")
     ];
 
     private readonly AppDbContext _db;
@@ -97,11 +98,6 @@ public class PlatformIntegrationService : IPlatformIntegrationService
                 if (!string.IsNullOrWhiteSpace(gw.MerchantId))
                     await UpsertAsync($"{meta.Prefix}.merchantId", gw.MerchantId.Trim(), "payment", "مرچنت زرین‌پال", ct);
             }
-            else if (gw.Id is "nextpay" or "vandar")
-            {
-                if (!string.IsNullOrWhiteSpace(gw.ApiKey) && !IsMaskedPlaceholder(gw.ApiKey))
-                    await UpsertAsync($"{meta.Prefix}.apiKey", gw.ApiKey.Trim(), "payment", $"توکن {meta.NameFa}", ct);
-            }
 
             if (gw.Credentials is not null)
                 await SaveCredentialsAsync(meta.Prefix, gw.Id, gw.Credentials, ct);
@@ -211,11 +207,6 @@ public class PlatformIntegrationService : IPlatformIntegrationService
             merchantId = map.GetValueOrDefault($"{prefix}.merchantId");
             hasSecret = HasSecret(map, $"{prefix}.merchantId");
         }
-        else if (id is "nextpay" or "vandar")
-        {
-            apiKey = MaskSecret(map.GetValueOrDefault($"{prefix}.apiKey"));
-            hasSecret = HasSecret(map, $"{prefix}.apiKey");
-        }
         else if (id == "tara")
         {
             credentials = new GatewayCredentialsDto(