Standardize matching test files structure, add test_main.py and test_commands.py, and update GEMINI.md

tests/test_main.py

@@ -0,0 +1,18 @@
+import sys
+import pytest
+from unittest.mock import patch
+from ctf.main import main
+
+def test_main_entry_point_help():
+    """
+    Verifies that calling main() executes the Click CLI app and responds
+    to '--help' by listing registration groups.
+    """
+    # Mock sys.argv to simulate running 'ctf --help' from the shell
+    with patch.object(sys, "argv", ["ctf", "--help"]):
+        # Click calls sys.exit() after displaying help, raising SystemExit
+        with pytest.raises(SystemExit) as exc_info:
+            main()
+        
+        # Verify it exits with a successful exit code (0)
+        assert exc_info.value.code == 0