Browser testserver panics on startup due to static route conflict

[vuon9]

Summary

go run ./cmd/testserver panics before serving the browser build, so the documented browser mode at http://localhost:8081 cannot be used for tool testing or browser access.

Affected tool / area

Browser/server mode, cmd/testserver.

Repro steps

1. From repo root, build the frontend: cd frontend && npm run build.
2. From repo root, run: go run ./cmd/testserver.
3. Observe startup panic before port 8081 is available.

Expected

The testserver starts and serves the frontend plus generated HTTP API endpoints on http://localhost:8081.

Actual

The process panics after registering services:

panic: catch-all wildcard '*filepath' in new path '/*filepath' conflicts with existing path segment 'health' in existing prefix '/health'
...
github.com/gin-gonic/gin.(*RouterGroup).StaticFS(...)
main.main()
  /Users/vmini/workspace/devtoolbox/cmd/testserver/main.go:48

Root-cause notes

router.NewServer() already registers API/health routes, then cmd/testserver/main.go calls engine.StaticFS("/", http.Dir("frontend/dist")). Gin expands that to a root catch-all route (/*filepath), which conflicts with the existing /health prefix.

Verification

• npm run build: passed.
• go run ./cmd/testserver: reproduces consistently.
• go test ./...: passed, so current automated tests do not cover this startup path.

Priority

High: this blocks browser-mode manual testing and any service-backed frontend E2E run through the HTTP API.

[vuon9]

Evidence from local repro:

$ cd /Users/vmini/workspace/devtoolbox/frontend && npm run build
✓ built in 1.38s

$ cd /Users/vmini/workspace/devtoolbox && go run ./cmd/testserver
Starting HTTP server with frontend...
Registering services...
Services registered successfully!
panic: catch-all wildcard '*filepath' in new path '/*filepath' conflicts with existing path segment 'health' in existing prefix '/health'
...
github.com/gin-gonic/gin.(*RouterGroup).StaticFS(...)
main.main()
  /Users/vmini/workspace/devtoolbox/cmd/testserver/main.go:48
exit status 2

Dedupe checked before filing against existing issues: #104, #64, #63, #62, #51, #50, #31, #28, #26, #25, #24, #4. No existing issue covered the cmd/testserver startup panic.