fix: install lamejs from GitHub repo for proper browser support

Switched from npm package to GitHub repo (github:zhuker/lamejs) which
includes the proper browser build. Reverted to simple dynamic import.

Fixes MP3 export MPEGMode reference error.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

package.json

@@ -11,7 +11,7 @@
   "dependencies": {
     "clsx": "^2.1.1",
     "fflate": "^0.8.2",
-    "lamejs": "^1.2.1",
+    "lamejs": "github:zhuker/lamejs",
     "lucide-react": "^0.553.0",
     "next": "^16.0.0",
     "react": "^19.0.0",