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/src/lib/styles/tokens.json

@@ -0,0 +1,34 @@
+{
+  "colors": {
+    "obsidian": "#14171A",
+    "iron": "#1E2228",
+    "slate": "#2C313A",
+    "pewter": "#3F4651",
+    "parchment": "#E8E4D8",
+    "vellum": "#C2BFB4",
+    "ash": "#9C9A92",
+    "moss": "#4A5D3F",
+    "bronze": "#8B7355",
+    "oxblood": "#6B2118",
+    "warning": "#8B6F1E",
+    "error": "#C04A1F",
+    "info": "#3D5A6E",
+    "accent": "#4A6B5C"
+  },
+  "radii": {
+    "sm": "4px",
+    "md": "8px",
+    "lg": "12px",
+    "xl": "16px"
+  },
+  "fonts": {
+    "display": "Fraunces",
+    "body": "Inter",
+    "mono": "JetBrains Mono"
+  },
+  "fontStacks": {
+    "display": "'Fraunces', Georgia, serif",
+    "body": "'Inter', system-ui, sans-serif",
+    "mono": "'JetBrains Mono', ui-monospace, monospace"
+  }
+}