Add scripts for environment setup and validation, and implement tests for portfolio performance exporter

- Created requirements.txt for dependencies including pandas, numpy, openpyxl, and yfinance.
- Added setup-env.sh script to set up a Python virtual environment and install required packages.
- Introduced validate-export.sh script to validate the exporter module and check expected fields.
- Implemented test cases in test_portfolio_performance_exporter.py to ensure correct CSV export functionality and data handling.

portfolio_performance_exporter.py

@@ -0,0 +1,48 @@
+"""Compatibility entry point for the XTB to Portfolio Performance export skill.
+
+The canonical implementation lives in
+`skills/xtb-portfolio-performance-export/scripts/exporter.py` so the skill
+folder can be copied and used standalone by an LLM agent. This shim preserves
+the repo API: `import portfolio_performance_exporter` and
+`python portfolio_performance_exporter.py`.
+"""
+from __future__ import annotations
+
+import importlib.util
+import sys
+from pathlib import Path
+
+
+_IMPL_PATH = (
+    Path(__file__).resolve().parent
+    / "skills"
+    / "xtb-portfolio-performance-export"
+    / "scripts"
+    / "exporter.py"
+)
+
+
+def _load_impl():
+    module_name = (
+        __name__
+        if __name__ != "__main__"
+        else "_xtb_portfolio_performance_exporter_impl"
+    )
+    script_dir = _IMPL_PATH.parent
+    if str(script_dir) not in sys.path:
+        sys.path.insert(0, str(script_dir))
+    spec = importlib.util.spec_from_file_location(module_name, _IMPL_PATH)
+    if spec is None or spec.loader is None:
+        raise ImportError(f"Could not load XTB Portfolio Performance implementation at {_IMPL_PATH}")
+    module = importlib.util.module_from_spec(spec)
+    sys.modules[module_name] = module
+    if __name__ != "__main__":
+        sys.modules[__name__] = module
+    spec.loader.exec_module(module)
+    return module
+
+
+_impl = _load_impl()
+
+if __name__ == "__main__":
+    _impl.main_cli()