fix: add Guid to string conversion in gRPC source generator

The MapToProtoModel function was silently failing when mapping Guid
properties to proto string fields, causing IDs to be empty in gRPC
responses. Added explicit Guid → string conversion handling.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Svrnty.CQRS.Grpc.Generators/Models/CommandInfo.cs

@@ -44,8 +44,11 @@ namespace Svrnty.CQRS.Grpc.Generators.Models
         public bool IsNullable { get; set; }
         public bool IsDecimal { get; set; }
         public bool IsDateTime { get; set; }
+        public bool IsGuid { get; set; }
+        public bool IsJsonElement { get; set; }
         public string? ElementType { get; set; }
         public bool IsElementComplexType { get; set; }
+        public bool IsElementGuid { get; set; }
         public List<PropertyInfo>? ElementNestedProperties { get; set; }
 
         public PropertyInfo()
@@ -61,7 +64,10 @@ namespace Svrnty.CQRS.Grpc.Generators.Models
             IsNullable = false;
             IsDecimal = false;
             IsDateTime = false;
+            IsGuid = false;
+            IsJsonElement = false;
             IsElementComplexType = false;
+            IsElementGuid = false;
         }
     }
 }