fix: restore inverse prefetch segment data routes for client segment cache
This restores the handling of routes without segment paths when clientSegmentCache
is enabled, which was removed in PR #82033. The inverse prefetch segment data routes
are necessary to prevent conflicts between dynamic routes when incremental PPR is used.
Without this logic, routes like /~/monitoring (PPR disabled) and /[teamSlug]/monitoring
(PPR enabled) can incorrectly match, causing client segment requests to route to the
wrong handler.
This reverts part of the optimization from #82033 to ensure proper route resolution
for apps using experimental.clientSegmentCache with incremental PPR.