docs(optimizr): add logo and fix rtd deps

docs/source/api/risk_metrics.md

@@ -0,0 +1,19 @@
+# API: Risk Metrics
+
+```python
+from optimizr import (
+    hurst_exponent_py,
+    compute_risk_metrics_py,
+    estimate_half_life_py,
+    bootstrap_returns_py,
+)
+
+h = hurst_exponent_py(returns)
+hl = estimate_half_life_py(returns)
+metrics = compute_risk_metrics_py(returns.tolist())
+boot = bootstrap_returns_py(returns, n_samples=1000)
+```
+
+- `returns`: 1D NumPy array of returns
+- `compute_risk_metrics_py` returns a dict with volatility, Sharpe, and drawdown estimates
+- `bootstrap_returns_py` resamples the series for uncertainty estimation