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.

skills/xtb-portfolio-performance-export/scripts/validate-export.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+if [[ -n "${PYTHON:-}" ]]; then
+  PYTHON_BIN="$PYTHON"
+elif [[ -x ".venv/bin/python" ]]; then
+  PYTHON_BIN=".venv/bin/python"
+else
+  PYTHON_BIN="python3"
+fi
+
+PYTHONDONTWRITEBYTECODE=1 "$PYTHON_BIN" - <<PY
+import importlib.util
+from pathlib import Path
+
+script = Path("$SCRIPT_DIR") / "exporter.py"
+spec = importlib.util.spec_from_file_location("xtb_portfolio_performance_exporter", script)
+module = importlib.util.module_from_spec(spec)
+spec.loader.exec_module(module)
+assert module.PORTFOLIO_FIELDS[0] == "Date"
+assert module.ACCOUNT_FIELDS[0] == "Date"
+print("Portfolio Performance exporter loaded")
+PY