feat: add Baostock A-share data source + validation report (25 stocks, 2021-2024)

[redamancy231-create]

Superseded by #35 — combined PR with GPT-5.6-Sol review fixes for VWAP, ticker case, neutralize guard, and comprehensive tests.

[initial-d]

There is one functional issue to fix before merge:

• _select_tickers() uppercases every manually supplied ticker. For --source baostock --tickers sh.600000,sz.000001, this produces SH.600000 / SZ.000001, while the Baostock loader and API require lowercase exchange prefixes. Please make ticker normalization source-aware (or preserve user input for Baostock) and add a focused regression test.

Please also correct the report wording: the data range ends in 2024, not 2025, and equal_weight is positive (+1.7%), so “All strategies negative or flat” is inaccurate.

[initial-d]

Thanks for adding the Baostock validation path and the A-share report. I amended the PR before merge to make the contribution safer and easier to reproduce:

• synced requirements.txt with the public-data loaders by adding yfinance and baostock
• normalized Baostock tickers to lowercase and added an explicit sh./sz. format check before calling the loader
• softened the report language so the A-share run is framed as reproducibility/validation evidence, not an alpha claim
• replaced the overstated "100% tradable" wording with download coverage
• removed the AI-tool co-author trailer from the commit metadata

CI is green on Python 3.9, 3.10, and 3.11.

[initial-d]

History maintenance note: main was rebuilt to correct the earlier #33 integration structure. The #34 content and final repository tree are unchanged. The reachable #34 merge commit is now 4309a34, with CI green on Python 3.9, 3.10, and 3.11.