fix(deps): override vulnerable MessagePack to 2.5.301 in AppHost

GHSA-hv8m-jj95-wg3x / CVE-2026-48109. Aspire.Hosting.PostgreSQL 13.2.1
pulls MessagePack 2.5.192 which is affected; pin the patched transitive
dependency explicitly.

src/GmRelay.AppHost/GmRelay.AppHost.csproj

@@ -8,6 +8,9 @@
 
   <ItemGroup>
     <PackageReference Include="Aspire.Hosting.PostgreSQL" Version="13.2.1" />
+    <!-- Overrides transitive vulnerable MessagePack 2.5.192 pulled by Aspire.Hosting.PostgreSQL.
+         See GHSA-hv8m-jj95-wg3x / CVE-2026-48109. -->
+    <PackageReference Include="MessagePack" Version="2.5.301" />
   </ItemGroup>
 
   <PropertyGroup>

src/GmRelay.AppHost/packages.lock.json

@@ -83,6 +83,16 @@
           "System.IO.Hashing": "10.0.3"
         }
       },
+      "MessagePack": {
+        "type": "Direct",
+        "requested": "[2.5.301, )",
+        "resolved": "2.5.301",
+        "contentHash": "WUnJgmYc06ngIxZxLe9sa0P6rOTyOZIQn8SuDvJSjyMn7e8/AdlNAdt81WPUhWKeQ7hDkgxKU1vTrJqX/4L79A==",
+        "dependencies": {
+          "MessagePack.Annotations": "2.5.301",
+          "Microsoft.NET.StringTools": "17.6.3"
+        }
+      },
       "SecurityCodeScan.VS2019": {
         "type": "Direct",
         "requested": "[5.6.7, )",
@@ -248,19 +258,10 @@
           "YamlDotNet": "16.3.0"
         }
       },
-      "MessagePack": {
-        "type": "Transitive",
-        "resolved": "2.5.192",
-        "contentHash": "Jtle5MaFeIFkdXtxQeL9Tu2Y3HsAQGoSntOzrn6Br/jrl6c8QmG22GEioT5HBtZJR0zw0s46OnKU8ei2M3QifA==",
-        "dependencies": {
-          "MessagePack.Annotations": "2.5.192",
-          "Microsoft.NET.StringTools": "17.6.3"
-        }
-      },
       "MessagePack.Annotations": {
         "type": "Transitive",
-        "resolved": "2.5.192",
+        "resolved": "2.5.301",
-        "contentHash": "jaJuwcgovWIZ8Zysdyf3b7b34/BrADw4v82GaEZymUhDd3ScMPrYd/cttekeDteJJPXseJxp04yTIcxiVUjTWg=="
+        "contentHash": "3PyBiSeKTfvtyzUv3+9eXGIw7vBBZ0GAc4k3+RVT0tz2vKv3l0pviiA2b6DrmHyDvj1Au8lSVDDw/wKPMxUQ4A=="
       },
       "Microsoft.Extensions.AI.Abstractions": {
         "type": "Transitive",