feat(nixos): manage scattered trash dirs with trash-cli retention timer (#265)

* feat(nushell): add trash command using the home trash can

On a tmpfs root with persistent dirs bind-mounted in, `rm --trash`
scatters items into per-mount .Trash-$uid dirs that file managers never
show, and gio refuses to trash on those internal mounts.

Add a `trash` command implementing the freedesktop trash spec
'failsafe' mode: items are moved to ~/.local/share/Trash with
spec-compliant .trashinfo entries, so Thunar can list and restore them.

Also preserve ~/.local/share/Trash on idols-ai so the trash survives
reboots.

* feat(nixos): manage scattered trash dirs with trash-cli retention timer

Replace the hand-written nushell trash command with the established
trash-cli tooling. On a tmpfs root with persistent dirs bind-mounted
in, the trash crate (nushell rm --trash) scatters items into per-mount
.Trash-$uid dirs that file managers never show and nothing cleans up.

- add trash-cli to system packages: trash-list scans/trash-restore
  handles every mount point's trash dir
- daily systemd timer runs 'trash-empty 30 -f', purging items older
  than 30 days across the home trash and all mount points
- drop the hand-written trash.nu module
- note in preservation.nix: do NOT persist ~/.local/share/Trash; a
  bind-mounted trash dir breaks the trash crate's home-topdir match
  for files straight under $HOME (it would try /.Trash-$uid, EACCES)

* fix(nixos): order trash-empty after preservation.target

The scattered .Trash-$uid dirs live inside the preservation bind
mounts, which use DefaultDependencies=no and are therefore NOT ordered
after local-fs.target. Add preservation.target to After= so trash-empty
only runs once all those mounts are up.

hosts/idols-ai/preservation.nix

@@ -110,6 +110,14 @@ in
         # Keep .cache off tmpfs to avoid high RAM usage; many apps use it and it is storage-heavy.
         ".cache"
 
+        # NOTE: do NOT persist ~/.local/share/Trash here. The trash crate (nushell
+        # `rm --trash`) picks the home trash only when the file's mount topdir equals
+        # the trash dir's topdir; a bind-mounted Trash dir would make files straight
+        # under $HOME fail with EACCES (it would try /.Trash-$uid). The home trash on
+        # tmpfs is lost on reboot, which is acceptable: scattered per-mount
+        # .Trash-$uid dirs on persistent volumes are covered by the trash-empty
+        # retention timer (modules/nixos/base/trash.nix).
+
         # ======================================
         # Codes / Work / Playground
         # ======================================