chore: scaffold Astro 5 project with token/style layer

- Astro 5 static config (trailing-slash canonical, i18n en-root/no-prefixed)
- Tailwind 4 over CSS custom-property tokens (both themes via [data-theme])
- design tokens: colour/spacing/type/radius/motion per Phase 1 specs
- motion layer with reduced-motion overrides
- strict TypeScript, ESLint flat config, Prettier
- self-hosted variable fonts (Space Grotesk / Inter / JetBrains Mono)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

site/eslint.config.js

@@ -0,0 +1,24 @@
+import js from '@eslint/js';
+import tseslint from 'typescript-eslint';
+import astro from 'eslint-plugin-astro';
+
+export default [
+  { ignores: ['dist/', '.astro/', 'node_modules/', '**/*.d.ts'] },
+  js.configs.recommended,
+  ...tseslint.configs.recommended,
+  ...astro.configs.recommended,
+  {
+    rules: {
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        { argsIgnorePattern: '^_', varsIgnorePattern: '^_' },
+      ],
+      '@typescript-eslint/consistent-type-imports': 'error',
+    },
+  },
+  {
+    // Behaviour modules run in the browser.
+    files: ['src/scripts/**/*.ts'],
+    languageOptions: { globals: { window: 'readonly', document: 'readonly', localStorage: 'readonly' } },
+  },
+];