Move proxy.ts into src when the /src directory is enabled
The Next.js template ships a proxy.ts that rewrites <page>.md and Accept: text/markdown requests to the Markdown route.
With the /src option, the CLI moved app, lib and components into src but left proxy.ts at the project root, where Next.js silently ignores it.
The CLI now moves proxy.ts (and the other root convention files Next.js reads next to app) into src, so the Markdown rewrite runs in generated projects.