refactor(web): extract design tokens to tokens.json source of truth

The Flutter client (#356) needs to consume the same FabledSword tokens
the web SPA uses. Move the data into a structured tokens.json file and
generate tokens.generated.css from it on every Vite build. The Flutter
side gets its own generator pointed at the same JSON.

No visual change — generated CSS matches the previous hand-written file.

Also installs @types/node devDependency: tsconfig already declared
"types": ["node"] but no Node builtins were referenced in TS until now,
so the missing types were latent. The new vite.config.ts plugin imports
node:child_process, surfacing the gap.

web/package.json

@@ -8,7 +8,8 @@
     "build": "vite build",
     "preview": "vite preview",
     "check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",
-    "test": "svelte-kit sync && vitest run"
+    "test": "svelte-kit sync && vitest run",
+    "tokens": "node scripts/tokens-to-css.js"
   },
   "devDependencies": {
     "@sveltejs/adapter-static": "^3.0.6",
@@ -16,6 +17,7 @@
     "@sveltejs/vite-plugin-svelte": "^4.0.0",
     "@testing-library/jest-dom": "^6.9.1",
     "@testing-library/svelte": "^5.3.1",
+    "@types/node": "^25.6.0",
     "autoprefixer": "^10.4.20",
     "jsdom": "^25.0.1",
     "postcss": "^8.4.49",