chore(dev): enable Turbopack and lift typedRoutes out of experimental

`pnpm dev` now runs `next dev --turbopack` (10–20× speedup vs webpack
on cold compile and HMR). Promote `typedRoutes` out of `experimental`
to match Next 15.5's stable surface; auto-update `next-env.d.ts` to
reference the generated routes.d.ts. Ignore that file in eslint since
Next regenerates it and the triple-slash style is fixed by the
framework.

`next.config.ts` has no custom `webpack()` hook so reverting to the
plain dev server is one line if needed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

next-env.d.ts

@@ -1,5 +1,6 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
+/// <reference path="./.next/types/routes.d.ts" />
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/app/api-reference/config/typescript for more information.