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

app/package.json

@@ -0,0 +1,48 @@
+{
+  "name": "app",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "build": "react-router build",
+    "dev": "react-router dev",
+    "start": "react-router-serve ./build/server/index.js",
+    "typecheck": "react-router typegen && tsc"
+  },
+  "dependencies": {
+    "@base-ui/react": "^1.3.0",
+    "@fontsource-variable/inter": "^5.2.8",
+    "@react-router/node": "7.14.0",
+    "@react-router/serve": "7.14.0",
+    "class-variance-authority": "^0.7.1",
+    "clsx": "^2.1.1",
+    "cmdk": "^1.1.1",
+    "date-fns": "^4.1.0",
+    "embla-carousel-react": "^8.6.0",
+    "input-otp": "^1.4.2",
+    "isbot": "^5.1.36",
+    "lucide-react": "^1.7.0",
+    "next-themes": "^0.4.6",
+    "radix-ui": "^1.4.3",
+    "react": "^19.2.4",
+    "react-day-picker": "^9.14.0",
+    "react-dom": "^19.2.4",
+    "react-resizable-panels": "^4.9.0",
+    "react-router": "7.14.0",
+    "recharts": "3.8.0",
+    "shadcn": "^4.2.0",
+    "sonner": "^2.0.7",
+    "tailwind-merge": "^3.5.0",
+    "tw-animate-css": "^1.4.0",
+    "vaul": "^1.1.2"
+  },
+  "devDependencies": {
+    "@react-router/dev": "7.14.0",
+    "@tailwindcss/vite": "^4.2.2",
+    "@types/node": "^22",
+    "@types/react": "^19.2.14",
+    "@types/react-dom": "^19.2.3",
+    "tailwindcss": "^4.2.2",
+    "typescript": "^5.9.3",
+    "vite": "^8.0.3"
+  }
+}