Handle noisy scanner posts before workshop router

[kentcdodds]

Summary

• Patch the packaged workshop app server during epicshop install so known scanner mutation probes are answered with a normal 404 before React Router reaches routes/$.
• Keep normal GET/HEAD/OPTIONS and all non-scanner app routes flowing through the existing router.
• Add a focused unit test for the postinstall patcher.

Sentry

• References epicshop issue EPICSHOP-F0 / 7447885629 (getInternalRouterError noise from POSTs to catch-all/splat scanner paths like /__rsc, /_next/image, /_rsc, /.action, /__nextjs_action, /_middleware, and /RSC/...txt).

Validation

• npm run test:patch-workshop-app --prefix ./epicshop
• npm ci (confirmed postinstall applies the workshop app server patch)
• npm run typecheck
• npm run lint
• node ./epicshop/test.js ..s
• Smoke test against npm start: scanner POSTs to /, /__rsc, /_next/image, /_rsc, /_next, /.action, /__nextjs_action, /_middleware, and /RSC/probe.txt returned normal 404 responses; POST /progress still routed normally.