feat: add myagents backends command (list supported agent backends)

tests/test_cli.py

@@ -40,6 +40,23 @@ class TestMyagentsHelp:
         assert result.exit_code == 0
         assert "Usage:" in result.output
 
+    def test_backends_lists_all(self) -> None:
+        """``myagents backends`` lists all supported agent backends."""
+        runner = CliRunner()
+        result = runner.invoke(cli, ["backends"])
+        assert result.exit_code == 0
+        assert "claude" in result.output
+        assert "kimi" in result.output
+        assert "codex" in result.output
+        assert "hermes" in result.output
+
+    def test_help_lists_backends(self) -> None:
+        """--help should list backends subcommand."""
+        runner = CliRunner()
+        result = runner.invoke(cli, ["--help"])
+        assert result.exit_code == 0
+        assert "backends" in result.output
+
 
 class TestClaudeSubcommand:
     """Tests for ``myagents claude``."""