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/tsconfig.json

@@ -0,0 +1,23 @@
+{
+  "extends": "astro/tsconfigs/strict",
+  "compilerOptions": {
+    "strict": true,
+    "noUncheckedIndexedAccess": true,
+    "noImplicitOverride": true,
+    "noFallthroughCasesInSwitch": true,
+    "verbatimModuleSyntax": true,
+    "allowJs": false,
+    "baseUrl": ".",
+    "paths": {
+      "@/*": ["src/*"],
+      "@i18n/*": ["src/i18n/*"],
+      "@components/*": ["src/components/*"],
+      "@layouts/*": ["src/layouts/*"],
+      "@styles/*": ["src/styles/*"],
+      "@scripts/*": ["src/scripts/*"],
+      "@lib/*": ["src/lib/*"]
+    }
+  },
+  "include": [".astro/types.d.ts", "src/**/*", "*.config.*"],
+  "exclude": ["dist", "node_modules"]
+}