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/tailwind.config.js

@@ -0,0 +1,20 @@
+export default {
+  content: ['./src/**/*.{html,js,ts,svelte}'],
+  darkMode: 'class',
+  theme: {
+    extend: {
+      colors: {
+        surface: {
+          900: '#14161a',
+          800: '#1a1d22',
+          700: '#2a2f36'
+        },
+        text: {
+          primary: '#e8ecf2',
+          secondary: '#cdd3db'
+        }
+      }
+    }
+  },
+  plugins: []
+};