Add StringSyntax attribute to Value property and fix sample code to use escaped quotes

Co-authored-by: stephentoub <[email protected]>

Author: Copilot

samples/AspNetCoreMcpServer/Tools/WeatherTools.cs

@@ -48,8 +48,8 @@ public async Task<string> GetAlerts(
     }
 
     [McpServerTool, Description("Get weather forecast for a location.")]
-    [McpMeta("category", "weather")]
-    [McpMeta("recommendedModel", "gpt-4")]
+    [McpMeta("category", "\"weather\"")]
+    [McpMeta("recommendedModel", "\"gpt-4\"")]
     public async Task<string> GetForecast(
         [Description("Latitude of the location.")] double latitude,
         [Description("Longitude of the location.")] double longitude)

src/ModelContextProtocol.Core/Server/McpMetaAttribute.cs

@@ -68,5 +68,6 @@ public McpMetaAttribute(string name, [StringSyntax(StringSyntaxAttribute.Json)]
     /// property to provide a JsonObject directly.
     /// </para>
     /// </remarks>
+    [StringSyntax(StringSyntaxAttribute.Json)]
     public string Value { get; }
 }