v2026.03.23.00

checkout: fix untracked->dir to be reported as UNTRACKED_ADDED

Summary:
When an untracked file was replaced by a directory in the destination commit, eden was reporting a MODIFIED_MODIFIED conflict, but this is not correct. The local file is not tracked, so cannot be modified. This messed up Sapling's expectations.

Step one is to fix eden to return the proper UNTRACKED_ADDED conflict type. Note that Sapling does not currently handle the file->directory path conflict situation here, but I will address that next.

Reviewed By: MichaelCuevas

Differential Revision: D96992296

fbshipit-source-id: 4f73f1612323897bb43c0dd1d0ac132ee275a766