Separate prerender outputs from route matchers
Prerendered routes currently serve both as render targets and as dynamic miss directives. Model those concerns independently so matcher-only entries do not need to masquerade as prerender outputs.
Legacy generateStaticParams behavior remains unchanged: fallback shells are emitted as outputs and represented by equivalent matcher directives when producing the prerender manifest.
Verification:
- pnpm --filter=next types
- pnpm test-start-turbo test/e2e/app-dir/sub-shell-generation/sub-shell-generation.test.ts
