feat(issue): add assigned_by filter to list_issues

Add an optional assigned_by parameter to the list_issues tool that maps to
gitea_sdk.ListIssueOption.AssignedBy, and include assignees in the slim
list_issues output for consistency with the single-issue view.

Co-Authored-By: Codet <codet@commitgo.dev> (GPT-5-Codex)

operation/issue/issue.go

@@ -49,6 +49,7 @@ var (
 		tool.Array("milestones", tool.Description("milestone name or ID filter"), tool.Items(map[string]any{"type": "string"})),
 		tool.String("since", tool.Description("updated after ISO 8601")),
 		tool.String("before", tool.Description("updated before ISO 8601")),
+		tool.String("assigned_by", tool.Description("filter by the user who assigned the issue")),
 		tool.Number("page", tool.Description(params.PageDesc), tool.Default(1)),
 		tool.Number("per_page", tool.Description(params.PaginationDesc), tool.Default(30)),
 	)
@@ -204,6 +205,9 @@ func listRepoIssuesFn(ctx context.Context, args map[string]any) (*mcp.CallToolRe
 	if t := params.GetOptionalTime(args, "before"); t != nil {
 		opt.Before = *t
 	}
+	if assignedBy, ok := args["assigned_by"].(string); ok {
+		opt.AssignedBy = assignedBy
+	}
 	client, err := gitea.ClientFromContext(ctx)
 	if err != nil {
 		return to.ErrorResult(fmt.Errorf("get gitea client err: %v", err))