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-lock.json

@@ -17,6 +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",
@@ -1334,6 +1335,16 @@
       "integrity": "sha512-dWHzHa2WqEXI/O1E9OjrocMTKJl2mSrEolh1Iomrv6U+JuNwaHXsXx9bLu5gG7BUWFIN0skIQJQ/L1rIex4X6w==",
       "license": "MIT"
     },
+    "node_modules/@types/node": {
+      "version": "25.6.0",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-25.6.0.tgz",
+      "integrity": "sha512-+qIYRKdNYJwY3vRCZMdJbPLJAtGjQBudzZzdzwQYkEPQd+PJGixUL5QfvCLDaULoLv+RhT3LDkwEfKaAkgSmNQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "undici-types": "~7.19.0"
+      }
+    },
     "node_modules/@types/trusted-types": {
       "version": "2.0.7",
       "resolved": "https://registry.npmjs.org/@types/trusted-types/-/trusted-types-2.0.7.tgz",
@@ -3764,6 +3775,13 @@
         "node": ">=14.17"
       }
     },
+    "node_modules/undici-types": {
+      "version": "7.19.2",
+      "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-7.19.2.tgz",
+      "integrity": "sha512-qYVnV5OEm2AW8cJMCpdV20CDyaN3g0AjDlOGf1OW4iaDEx8MwdtChUp4zu4H0VP3nDRF/8RKWH+IPp9uW0YGZg==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/update-browserslist-db": {
       "version": "1.2.3",
       "resolved": "https://registry.npmjs.org/update-browserslist-db/-/update-browserslist-db-1.2.3.tgz",