build: raise Node heap for production build

The production build renders thousands of modules and exceeds V8's
default heap ceiling, so `npm run build` fails with a JavaScript
heap out-of-memory error during "rendering chunks". Set
NODE_OPTIONS=--max-old-space-size=8192 on the Vite build step via
cross-env (kept portable for Windows), so a fresh clone builds
without any manual environment setup. Document the matching Docker
memory requirement in DOCKER.md, since the container build hits the
same limit when the Docker VM has too little RAM.

package.json

@@ -5,7 +5,7 @@
   "type": "module",
   "scripts": {
     "dev": "vite",
-    "build": "tsc && vite build",
+    "build": "tsc && cross-env NODE_OPTIONS=--max-old-space-size=8192 vite build",
     "lint": "eslint -c .eslintrc.json ./src/**/**/*.{ts,tsx} --fix",
     "preview": "vite preview"
   },
@@ -88,6 +88,7 @@
     "@typescript-eslint/parser": "8.11.0",
     "@vitejs/plugin-react": "^4.2.1",
     "autoprefixer": "10.4.19",
+    "cross-env": "^7.0.3",
     "esbuild": "^0.28.0",
     "eslint": "^8.57.0",
     "eslint-config-prettier": "9.1.0",