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>

package.json

@@ -4,7 +4,7 @@
   "private": true,
   "packageManager": "pnpm@10.33.2",
   "scripts": {
-    "dev": "next dev",
+    "dev": "next dev --turbopack",
     "build": "next build && pnpm build:server",
     "build:server": "esbuild src/server.ts --bundle --platform=node --target=node20 --format=cjs --outdir=dist --packages=external --tsconfig=tsconfig.server.json",
     "build:worker": "esbuild src/worker.ts --bundle --platform=node --target=node20 --format=cjs --outdir=dist --packages=external --tsconfig=tsconfig.server.json",