Fix nil pointer dereference in completion handler

The CompleteParams.Context field is optional (marked omitempty) and can be
nil when clients don't send it. The code was accessing Context.Arguments
directly without checking if Context was nil first, causing a panic.

This fix adds a nil check for Context before accessing Arguments.

Author: SamMorrowDrums

pkg/github/repository_resource_completions.go

@@ -33,8 +33,10 @@ func RepositoryResourceCompletionHandler(getClient GetClientFn) func(ctx context
 
 		argName := req.Params.Argument.Name
 		argValue := req.Params.Argument.Value
-		resolved := req.Params.Context.Arguments
-		if resolved == nil {
+		var resolved map[string]string
+		if req.Params.Context != nil && req.Params.Context.Arguments != nil {
+			resolved = req.Params.Context.Arguments
+		} else {
 			resolved = map[string]string{}
 		}