docs(optimizr): add logo and fix rtd deps

docs/source/api/optimal_control.md

@@ -0,0 +1,23 @@
+# API: Optimal Control / Kalman
+
+Control utilities are exposed through the Rust extension (`optimizr._core`).
+
+```python
+from optimizr import maths_toolkit
+
+if maths_toolkit is None:
+    raise RuntimeError("Rust backend missing; reinstall with `pip install .`.")
+
+# Initialize a Kalman filter
+kf = maths_toolkit.init_kalman_filter(F, H, Q, R)
+state = maths_toolkit.kalman_predict(kf, x0)
+state = maths_toolkit.kalman_update(kf, state, observation)
+```
+
+Parameters
+- `F`: state transition matrix (list of lists)
+- `H`: observation matrix
+- `Q`: process noise covariance
+- `R`: observation noise covariance
+
+Also see the Mean Field Games API in `mean_field_games.md`.