preflight: retire the .next generated-state certification (#1444)

CI's test step caught the gap: sourceFingerprint resolved
next/package.json from apps/web, which P5 removed. The certification
(fingerprint incl. @next/env expansion, symlink manifest, foreign-uid
scan, build lock) defended typecheck against stale apps/web/.next
output; the Vite SPA has no generated tree later gates consume, so the
class it defended against is gone. Preflight keeps its other job, the
missing-binaries check with exit 42. clean-generated.mjs (a .next
quarantine helper) goes with it.

package.json

@@ -7,7 +7,6 @@
     "dev": "turbo run dev",
     "lint": "turbo run lint",
     "preflight": "node scripts/preflight.mjs",
-    "clean:generated": "node scripts/clean-generated.mjs",
     "typecheck": "pnpm preflight && turbo run typecheck",
     "verify:release": "node scripts/verify-release.mjs",
     "test:checkout": "node --test scripts/*.test.mjs",