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.

modules/base/packages.nix

@@ -86,5 +86,6 @@
     which
     tree
     tealdeer # a very fast version of tldr
+    trash-cli # freedesktop trash can CLI: trash-list / trash-restore / trash-put / trash-empty
   ];
 }