feat: Replace build.py with JSX-based webpack-native book index generation

Port the Python HTML-generation script to a React component (src/BookIndex.jsx)
rendered at build time via renderToStaticMarkup, removing the need to run
build.py separately before webpack.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -4,12 +4,17 @@
     "dev": "webpack serve --mode=development"
   },
   "devDependencies": {
+    "@babel/core": "^7.29.7",
+    "@babel/preset-react": "^7.29.7",
+    "@babel/register": "^7.29.7",
     "copy-webpack-plugin": "^14.0.0",
     "css-loader": "^7.1.4",
     "css-minimizer-webpack-plugin": "^8.0.0",
     "html-webpack-plugin": "^5.6.7",
     "mini-css-extract-plugin": "^2.10.2",
     "prettier": "^3.8.3",
+    "react": "^19.2.7",
+    "react-dom": "^19.2.7",
     "style-loader": "^4.0.0",
     "webpack": "^5.107.2",
     "webpack-cli": "^7.0.3",