feat(frontend): scaffold SvelteKit + Tailwind with landing (part 1)

New SvelteKit app in frontend/ (minimal template, TypeScript, TailwindCSS v4).
Adds the app shell (dark music theme navbar + footer) and a landing page with
hero and feature cards. CTAs point to /login and /explore (built in later parts).

Verified: production build succeeds and the page renders with Tailwind styles
applied (checked via preview).

frontend/vite.config.ts

@@ -0,0 +1,21 @@
+import tailwindcss from '@tailwindcss/vite';
+import adapter from '@sveltejs/adapter-auto';
+import { sveltekit } from '@sveltejs/kit/vite';
+import { defineConfig } from 'vite';
+
+export default defineConfig({
+	plugins: [
+		tailwindcss(),
+		sveltekit({
+			compilerOptions: {
+				// Force runes mode for the project, except for libraries. Can be removed in svelte 6.
+				runes: ({ filename }) => filename.split(/[/\\]/).includes('node_modules') ? undefined : true
+			},
+
+			// adapter-auto only supports some environments, see https://svelte.dev/docs/kit/adapter-auto for a list.
+			// If your environment is not supported, or you settled on a specific environment, switch out the adapter.
+			// See https://svelte.dev/docs/kit/adapters for more information about adapters.
+			adapter: adapter()
+		})
+	]
+});