Prepare product layout and reusable Flutter theme

Relocate the existing Astro website and preserve its assets and hosting configuration. Add the consumer/backend scaffold and themed Flutter package with consumer tests. Related to #1.

website/scripts/generate-tokens.mjs

@@ -0,0 +1,14 @@
+import { readFileSync, writeFileSync } from 'node:fs';
+const tokens = JSON.parse(
+  readFileSync(new URL('../design/tokens.json', import.meta.url), 'utf8'),
+);
+const kebab = (name) => name.replace(/[A-Z]/g, (c) => `-${c.toLowerCase()}`);
+const colors = Object.entries(tokens.colors);
+writeFileSync(
+  new URL('../src/styles/tokens.css', import.meta.url),
+  `/* Generated by npm run tokens. Edit design/tokens.json. */\n:root {\n${colors.map(([k, v]) => `  --${kebab(k)}: ${v};`).join('\n')}\n  --radius: ${tokens.website.radius.card}px;\n  --font-family: '${tokens.typography.family}', Arial, sans-serif;\n}\n`,
+);
+writeFileSync(
+  new URL('../flutter/brand_palette.dart', import.meta.url),
+  `// Generated brand palette reference. Optional for the Flutter application.\n// This is not an application theme: choose component styling independently.\nimport 'dart:ui';\n\nabstract final class SxchngeBrand {\n${colors.map(([k, v]) => `  static const ${k} = Color(0xFF${v.slice(1).toUpperCase()});`).join('\n')}\n  static const fontFamily = '${tokens.typography.family}';\n}\n`,
+);