Browser mode root returns 404 in built app

[vuon9]

Severity

P1

Affected area

Built app browser mode / HTTP server

Build/run evidence

Built from source on 2026-05-27:

cd frontend && bun run build
cd ..
go build -o bin/DevToolbox-discovery .
./bin/DevToolbox-discovery

The built app starts the HTTP API on localhost:8081 and /health works:

{"mode":"web","status":"ok"}

Repro

1. Build and run the app from source.
2. Open or request http://localhost:8081/.
3. Compare with README/docs that say browser mode is available at http://localhost:8081 when the desktop app is running.

Actual

GET / on localhost:8081 returns 404 Not Found.

Expected

Either the browser UI should be served at http://localhost:8081/, or the docs should clearly say browser UI requires serving the built frontend separately while the API runs on 8081.

Notes

This is not the same as #107. That issue is about the browser testserver panicking on startup due to a static route conflict; this issue is about the built desktop app's HTTP server not serving the browser UI at the documented root.