docs(notebooks): topology + BSDE notebook improvements

- 07_topology: expanded persistent-homology examples
- 10_bsde: reworked BSDE solver walkthrough
- 04/05: clear execution counts
- gitignore generated plot PNGs (docs snippets + notebook frames)

examples/notebooks/04_real_world_applications.ipynb

@@ -367,7 +367,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 6,
+   "execution_count": null,
    "id": "d3f64621",
    "metadata": {
     "execution": {
@@ -411,7 +411,7 @@
     "axes[0].set_title('True Market Regimes', fontsize=14, fontweight='bold')\n",
     "axes[0].legend()\n",
     "axes[0].grid(alpha=0.3)\n",
-    "\n",
+    " \n",
     "# Plot 2: Predicted regimes\n",
     "for regime_name in ['Bull', 'Bear', 'Neutral']:\n",
     "    mask = df_btc['predicted_regime_name'] == regime_name\n",