feat: enable route-consistent screen audio stereo [skip ci]

Merge reviewed audio quality improvement after video quality-tier production cutover. Production deployment follows exact merged SHA.

package.json

@@ -28,6 +28,7 @@
     "lucide-react": "1.31.0",
     "react": "19.2.8",
     "react-dom": "19.2.8",
+    "sdp-transform": "2.15.0",
     "sirv": "3.0.2",
     "ws": "8.21.3",
     "zod": "4.4.3"
@@ -36,6 +37,7 @@
     "@types/node": "24.13.3",
     "@types/react": "19.2.18",
     "@types/react-dom": "19.2.4",
+    "@types/sdp-transform": "2.15.0",
     "@types/ws": "8.18.1",
     "@vitejs/plugin-react": "6.0.5",
     "tsx": "4.23.12",