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/.vscode/extensions.json

@@ -0,0 +1,6 @@
+{
+	"recommendations": [
+		"svelte.svelte-vscode",
+		"bradlc.vscode-tailwindcss"
+	]
+}

frontend/.vscode/settings.json

@@ -0,0 +1,5 @@
+{
+	"files.associations": {
+		"*.css": "tailwindcss"
+	}
+}