Install: staging and sd:/ are on the same card, so pack folders are now
moved with f_rename (a missing target folder moves in one step, existing
ones are merged file by file). Copying is only a per-entry fallback.
The staging cleanup afterwards only removes empty folders.
Deletion: one f_stat per list entry, no full recursive count before
deleting; large folders are detected with a probe that stops after 51
entries. Progress lines count processed entries instead of needing an
extra pass for a total.
Six copy/delete walkers (fs.c + install.c) are replaced by fs_delete_tree,
fs_move_tree and fs_move_file sharing one path buffer and one copy buffer
per run; the 'alternative copy method' retry is gone. extras/hekate-ams-pro
is moved too. Backups keep copy semantics.