fix: Fixed app.py

- Replaced NULL with None
- Added proper error handling with typer.BadParameter
- Added if __name__ == '__main__' block

app.py

@@ -0,0 +1,14 @@
+import typer
+
+app = typer.Typer()
+
+
+@app.command()
+def start(config_path: str = None):
+    if config_path is None:
+        raise typer.BadParameter("No config file path provided")
+    # TODO: config validation, run app, run tests
+
+
+if __name__ == "__main__":
+    app()