fix(iab): correct Myket purchase verification to the documented POST /verify API

Myket's server-to-server validation is POST
/api/partners/applications/{pkg}/purchases/products/{sku}/verify with the
purchase token in the JSON body ({"tokenId": ...}) + X-Access-Token header —
not a GET with the token in the path. purchaseState 0 = valid.
Ref: https://myket.ir/kb/pages/server-to-server-payment-validation-api/

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

server/src/Hokm.Server/Payments/IabService.cs

@@ -110,19 +110,26 @@ public sealed class IabService
     }
 
     /// <summary>
-    /// Myket: validate via the developer API (mirrors Google Play). The access
-    /// token comes from the Myket developer panel.
+    /// Myket: validate via the developer API. POST the purchase token in the body
+    /// (`{ "tokenId": ... }`) to the partners/verify endpoint with an X-Access-Token
+    /// header. The access token comes from the Myket developer panel → in-app
+    /// products. See https://myket.ir/kb/pages/server-to-server-payment-validation-api/
     /// </summary>
     private async Task<bool> VerifyMyket(string productId, string token)
     {
         if (string.IsNullOrWhiteSpace(_opts.MyketAccessToken)) return _opts.AllowUnverified;
 
-        var url = $"https://developer.myket.ir/api/applications/{_opts.PackageName}/purchases/products/{Uri.EscapeDataString(productId)}/tokens/{Uri.EscapeDataString(token)}";
-        using var req = new HttpRequestMessage(HttpMethod.Get, url);
+        var url = $"https://developer.myket.ir/api/partners/applications/{_opts.PackageName}/purchases/products/{Uri.EscapeDataString(productId)}/verify";
+        using var req = new HttpRequestMessage(HttpMethod.Post, url);
         req.Headers.Add("X-Access-Token", _opts.MyketAccessToken);
+        req.Content = new StringContent(
+            JsonSerializer.Serialize(new { tokenId = token }),
+            System.Text.Encoding.UTF8,
+            "application/json");
         var resp = await Http.SendAsync(req);
         if (!resp.IsSuccessStatusCode) return false;
         using var doc = JsonDocument.Parse(await resp.Content.ReadAsStringAsync());
+        // purchaseState: 0 = successful purchase, 1 = failed.
         if (doc.RootElement.TryGetProperty("purchaseState", out var ps) && ps.ValueKind == JsonValueKind.Number)
             return ps.GetInt32() == 0;
         return true;