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/src/app.css

@@ -0,0 +1,13 @@
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+:root {
+  color-scheme: dark;
+}
+
+html,
+body {
+  height: 100%;
+  margin: 0;
+}