feat(web): scaffold SvelteKit SPA with Tailwind + adapter-static

- SvelteKit 2.x + Svelte 5 + TypeScript + Vite 5
- adapter-static with fallback:'index.html' for SPA deep-link routing
- Tailwind configured with dark-only palette matching spec
- Placeholder landing page at /
- Committed web/build/index.html placeholder (via .gitignore negation) so
  go:embed works before the SvelteKit build has been run

web/postcss.config.cjs

@@ -0,0 +1,6 @@
+module.exports = {
+  plugins: {
+    tailwindcss: {},
+    autoprefixer: {}
+  }
+};