Add BaiQuant real-world Codex case study

[bkidy]

Summary

• Add a real-world Codex case study to Tutorials & Articles.
• The article documents a 24-hour Codex Goal that turned an open-ended finance objective into data ingestion, backtesting, risk rules, and the open-source BaiQuant strategy.

Why it fits

This is a first-hand production workflow rather than a general AI overview. The article explains both the useful outcome and the limits: market conditions, overfitting risk, execution constraints, and why short-term return is feedback rather than proof.

Checks

• Article URL returns HTTP 200.
• Entry follows the existing one-line article format.
• No duplicate BaiQuant or equivalent case-study entry is present.