fix(skills): remove phantom resource references and fix CoC links (#447)

Remove references to non-existent resource files (references/, assets/,
scripts/, examples/) from 115 skill SKILL.md files. These sections
pointed to directories and files that were never created, causing
confusion when users install skills.

Also fix broken Code of Conduct links in issue templates to use
absolute GitHub URLs instead of relative paths that 404.

plugins/quantitative-trading/skills/backtesting-frameworks/SKILL.md

@@ -655,9 +655,3 @@ def calculate_metrics(returns: pd.Series, rf_rate: float = 0.02) -> Dict[str, fl
 - **Don't use adjusted data carelessly** - Understand adjustments
 - **Don't optimize on full history** - Reserve test set
 - **Don't ignore capacity** - Market impact matters
-
-## Resources
-
-- [Advances in Financial Machine Learning (Marcos López de Prado)](https://www.amazon.com/Advances-Financial-Machine-Learning-Marcos/dp/1119482089)
-- [Quantitative Trading (Ernest Chan)](https://www.amazon.com/Quantitative-Trading-Build-Algorithmic-Business/dp/1119800064)
-- [Backtrader Documentation](https://www.backtrader.com/docu/)

plugins/quantitative-trading/skills/risk-metrics-calculation/SKILL.md

@@ -549,9 +549,3 @@ for metric, value in summary.items():
 - **Don't ignore correlation** - Increases in stress
 - **Don't use short lookbacks** - Miss regime changes
 - **Don't forget transaction costs** - Affects realized risk
-
-## Resources
-
-- [Risk Management and Financial Institutions (John Hull)](https://www.amazon.com/Risk-Management-Financial-Institutions-5th/dp/1119448115)
-- [Quantitative Risk Management (McNeil, Frey, Embrechts)](https://www.amazon.com/Quantitative-Risk-Management-Techniques-Princeton/dp/0691166277)
-- [pyfolio Documentation](https://quantopian.github.io/pyfolio/)