Use emitted app entries for post-build processing (#97139)
Route discovery currently feeds app page keys both into compilation and
into post-build work like adapters and standalone output. This instead
filters the discovered keys against app-paths-manifest after compilation
and uses that emitted set for post-build processing. Today every
discovered app entry is emitted, so this does not change behavior. It
just makes the build output, rather than the earlier discovery input,
the source of truth for work that happens after compilation.
