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/SKILL.md

@@ -0,0 +1,43 @@
+---
+name: xtb-portfolio-performance-export
+description: Use when converting XTB brokerage .xlsx exports to Portfolio Performance-compatible CSV files, validating Portfolio Transactions and Account Transactions outputs, or explaining the Portfolio Performance import workflow.
+---
+
+# XTB Portfolio Performance Export
+
+Use this skill to create and validate Portfolio Performance CSV files from XTB
+`Cash Operations` data using the bundled `exporter.py`.
+
+## Workflow
+
+1. Identify the target workbook. If omitted and exactly one non-lock `.xlsx`
+   exists, the exporter can auto-detect it.
+2. Run exporter validation before trusting an import file:
+   `<skill-folder>/scripts/validate-export.sh`
+3. Create the Portfolio Performance CSV files:
+   `<skill-folder>/scripts/export-portfolio-performance.sh <report.xlsx>`
+4. If the user needs a custom directory, run:
+   `<skill-folder>/scripts/export-portfolio-performance.sh <report.xlsx> -o <output-dir>`
+5. Inspect the generated CSV headers and a sample of rows before saying they
+   are import-ready.
+6. Read `references/portfolio-performance-csv.md` before explaining import
+   steps, transaction mappings, or limitations.
+
+## Outputs
+
+- `results/<stem>_portfolio_performance_portfolio_transactions.csv`
+- `results/<stem>_portfolio_performance_account_transactions.csv`
+
+## Guardrails
+
+- Import Portfolio Transactions before Account Transactions so securities
+  exist before dividend rows are matched.
+- Use UTF-8, semicolon delimiter, and first-line header in Portfolio
+  Performance.
+- Refer to Portfolio Performance UI accounts as `Deposit Account` and
+  `Securities Account`; keep CSV field names literal as `Cash Account` and
+  `Securities Account`.
+- Do not claim the generated files are fully imported until the user has
+  reviewed Portfolio Performance's wizard preview/status column.
+- Keep multi-currency caveats visible: this first exporter uses the account
+  currency and deterministic account labels, with optional CLI overrides.