Remove json tags from internal structs

JSON marshaling uses field names directly; explicit tags
are unnecessary at this level.

Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>

pkg/agent/tool.go

@@ -25,8 +25,8 @@ import (
 
 type (
 	ToolResult struct {
-		Content string `json:"content"`
-		IsError bool   `json:"is_error"`
+		Content string
+		IsError bool
 	}
 
 	// ToolDescriptor describes a tool's name and LLM definition.