Chapter 9 - Medians and Order Statistics

This legacy guide forwards to the native fourth-edition Chapter 9 guide CLRSLean.FourthEdition.Chapter_09. The third-edition-numbered section imports CLRSLean.Chapter_09.Section_09_* (including the randomized-SELECT support page) also forward to the native fourth-edition sources during the compatibility period (see docs/migrations/clrs4.md).