fix broken references to deleted files, remove dead code

Build-breaking fixes:
- kibbeh: remove imports of deleted admin-essentials, nix, zsh configs
  (all provided by niphas via profiles.default + profiles.desktop)
- tabula, tahina: remove imports of deleted admin-essentials, nix configs
  (provided by niphas via profiles.default)
- zaatar: remove import of deleted tmux config
  (provided by niphas via profiles.default)

Dead code removal:
- flake.nix: remove nixosModules.zsh-kmein (referenced deleted config/zsh.nix)
- flake.nix: remove unused wallpapers input
- packages/gpt.nix, hora.nix, k-lock.nix: orphaned, not in overlay or referenced
- configs/hledger.nix: remove hora reference (package deleted)

configs/hledger.nix

@@ -4,7 +4,6 @@
 }:
 let
   ledgerDirectory = "/home/kfm/sync/src/ledger";
-  hora = pkgs.callPackage ../packages/hora.nix { timeLedger = "${ledgerDirectory}/time.timeclock"; };
 in
 {
   environment.systemPackages =
@@ -12,7 +11,6 @@ in
       git = "${pkgs.git}/bin/git -C ${ledgerDirectory}";
     in
     [
-      hora
       pkgs.hledger
       (pkgs.writers.writeDashBin "hledger-git" ''
         if [ "$1" = entry ]; then