fix: Match argument case when displaying errors for missing CLI arguments

src/google/adk/cli/cli_tools_click.py

@@ -59,6 +59,19 @@ class HelpfulCommand(click.Command):
 
   def __init__(self, *args, **kwargs):
     super().__init__(*args, **kwargs)
+
+  @staticmethod
+  def _format_missing_arg_error(click_exception):
+    """Format the missing argument error with uppercase parameter name.
+
+    Args:
+      click_exception: The MissingParameter exception from Click.
+
+    Returns:
+      str: Formatted error message with uppercase parameter name.
+    """
+    name = click_exception.param.name
+    return f"Missing required argument: {name.upper()}"
 
   def parse_args(self, ctx, args):
     """Override the parse_args method to show help text on error.
@@ -77,8 +90,10 @@ def parse_args(self, ctx, args):
     try:
       return super().parse_args(ctx, args)
     except click.MissingParameter as exc:
+      error_message = self._format_missing_arg_error(exc)
+
       click.echo(ctx.get_help())
-      click.secho(f"\nError: {str(exc)}", fg="red", err=True)
+      click.secho(f"\nError: {error_message}", fg="red", err=True)
       ctx.exit(2)