docs(optimizr): add logo and fix rtd deps

docs/source/api/sparse.md

@@ -0,0 +1,26 @@
+# API: Sparse Optimization
+
+## sparse_pca_py
+```python
+from optimizr import sparse_pca_py
+
+components = sparse_pca_py(
+    X,
+    n_components=3,
+    l1_ratio=0.2,
+)
+```
+- `X`: 2D NumPy array
+- Returns component matrix `(n_components, n_features)`
+
+## box_tao_decomposition_py
+```python
+from optimizr import box_tao_decomposition_py
+solution = box_tao_decomposition_py(X)
+```
+
+## elastic_net_py
+```python
+from optimizr import elastic_net_py
+coeffs = elastic_net_py(X, y, l1_ratio=0.3, alpha=0.01)
+```