feat: nginx reverse proxy, Spotify import, overlay system, UI overhaul

- Add nginx as single entry point: /api/* → backend, /* → web
- NEXT_PUBLIC_API_URL="" so all API calls are relative (go through nginx)
- Add Spotify playlist import (Client Credentials OAuth, up to 500 tracks)
- Add Yandex/Spotify tabbed import UI on /playlists
- Add stream overlay system (SSE + polling fallback, 9 styles)
- Reorganize pages into (main) route group
- Add QueuePanel, VersionsPanel, Toaster components
- Add overlay settings tab in /settings

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/tsconfig.json

@@ -1,6 +1,10 @@
 {
   "compilerOptions": {
-    "lib": ["dom", "dom.iterable", "esnext"],
+    "lib": [
+      "dom",
+      "dom.iterable",
+      "esnext"
+    ],
     "allowJs": true,
     "skipLibCheck": true,
     "strict": true,
@@ -12,9 +16,25 @@
     "isolatedModules": true,
     "jsx": "preserve",
     "incremental": true,
-    "plugins": [{ "name": "next" }],
-    "paths": { "@/*": ["./src/*"] }
+    "plugins": [
+      {
+        "name": "next"
+      }
+    ],
+    "paths": {
+      "@/*": [
+        "./src/*"
+      ]
+    },
+    "target": "ES2017"
   },
-  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx", ".next/types/**/*.ts"],
-  "exclude": ["node_modules"]
+  "include": [
+    "next-env.d.ts",
+    "**/*.ts",
+    "**/*.tsx",
+    ".next/types/**/*.ts"
+  ],
+  "exclude": [
+    "node_modules"
+  ]
 }