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/references/portfolio-performance-csv.md

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+# Portfolio Performance CSV Mapping
+
+Load this when validating or explaining XTB to Portfolio Performance exports.
+
+## Generated Files
+
+- `<stem>_portfolio_performance_portfolio_transactions.csv`
+  - Import type: `Portfolio Transactions`
+  - Header: `Date;Type;Shares;Ticker Symbol;Security Name;Value;Fees;Taxes;Note;Securities Account;Cash Account`
+- `<stem>_portfolio_performance_account_transactions.csv`
+  - Import type: `Account Transactions`
+  - Header: `Date;Type;Value;Ticker Symbol;Security Name;Shares;Gross Amount;Currency Gross Amount;Note;Cash Account;Offset Account`
+
+Both files are UTF-8 CSV files with semicolon delimiters and a first-line
+header.
+
+Portfolio Performance's UI uses `Deposit Accounts` for cash/deposit accounts
+and `Securities Accounts` for custody accounts. The CSV importer still names
+the deposit-account field `Cash Account`; keep that header literal.
+
+## XTB To Portfolio Performance Mapping
+
+- `Stock purchase` or `OPEN BUY` -> Portfolio `Buy`
+- `Stock sale`, `Stock sell`, `CLOSE SELL`, or `OPEN SELL` -> Portfolio `Sell`
+- `Stock sell` with `CLOSE BUY` -> Portfolio `Sell`
+- `Deposit` -> Account `Deposit`
+- `Withdrawal` -> Account `Withdrawal`
+- `Dividend` -> Account `Dividend`
+- `Dividend tax`, `RO tax`, `Free funds interest tax`, or other tax-like rows -> Account `Taxes`
+- `Free funds interest` -> Account `Interest`
+- `Currency conversion` -> Account `Fees`
+- `Subaccount transfer` or `Transfer` -> Account `Transfer (Inbound)` or `Transfer (Outbound)` by amount sign
+
+## Import Steps
+
+1. In Portfolio Performance, create or open the target portfolio file.
+2. Ensure the Portfolio Performance `Securities Account` and `Deposit Account`
+   exist, or select/create them in the import wizard. The default CSV names are
+   `XTB` and `XTB (<CCY>)`.
+3. Import the portfolio transactions CSV first with `File > Import > CSV files`.
+4. Select type `Portfolio Transactions`.
+5. Use `UTF-8`, delimiter `semicolon`, and enable `First line contains header`.
+6. Confirm mappings for `Date`, `Type`, `Shares`, `Ticker Symbol`,
+   `Security Name`, `Value`, `Fees`, `Taxes`, `Securities Account`, and
+   `Cash Account`. In the CSV importer, `Cash Account` maps to the Portfolio
+   Performance deposit account.
+7. Finish that import and resolve any security matching prompts.
+8. Import the account transactions CSV with `File > Import > CSV files`.
+9. Select type `Account Transactions`.
+10. Use the same CSV settings: `UTF-8`, semicolon delimiter, first line header.
+11. Confirm mappings for `Date`, `Type`, `Value`, `Ticker Symbol`,
+    `Security Name`, `Shares`, `Gross Amount`, `Currency Gross Amount`,
+    `Cash Account`, and `Offset Account`. In the CSV importer, `Cash Account`
+    maps to the Portfolio Performance deposit account.
+12. Review the preview/status column before finishing, especially transfers,
+    taxes, and dividends.
+
+## Limitations
+
+- The exporter does not create Portfolio Performance `.xml` portfolio files.
+- It does not generate Portfolio Performance JSON import configurations.
+- Multi-currency gross amount and exchange-rate fields are left blank unless a
+  future XTB mapping can populate them safely.