refactor(app): extract previewChords to song-utils, simplify API_BASE, fix useEffect deps and cleanup

app/vite.config.ts

@@ -0,0 +1,10 @@
+import { reactRouter } from "@react-router/dev/vite";
+import tailwindcss from "@tailwindcss/vite";
+import { defineConfig } from "vite";
+
+export default defineConfig({
+  plugins: [tailwindcss(), reactRouter()],
+  resolve: {
+    tsconfigPaths: true,
+  },
+});