feat(desktop): thunar and the moonarch zshrc

Both were missing against the Arch package set: thunar with volman and the
archive plugin, tumbler and ffmpegthumbnailer (packages/official.txt:79-83),
and defaults/shell/zshrc, which Arch installs as /etc/zsh/zshrc.moonarch.

modules/desktop.nix

@@ -123,6 +123,22 @@ in
   # --- Shell ---
   programs.zsh.enable = true;
 
+  # Same file the Arch package installs as /etc/zsh/zshrc.moonarch. zsh reads
+  # /etc/zshrc before ~/.zshrc, so a user file still wins over it.
+  programs.zsh.interactiveShellInit = ''
+    source ${moonarchSrc}/defaults/shell/zshrc
+  '';
+
+  # --- File manager ---
+  #
+  # Counterpart to thunar, thunar-volman, thunar-archive-plugin, tumbler and
+  # ffmpegthumbnailer in packages/official.txt.
+  programs.thunar = {
+    enable = true;
+    plugins = with pkgs; [ thunar-volman thunar-archive-plugin ];
+  };
+  services.tumbler.enable = true;
+
   # --- Theme, systemwide instead of the gsettings calls in post-install.sh ---
   programs.dconf = {
     enable = true;
@@ -188,10 +204,12 @@ in
     networkmanagerapplet
     blueman
 
-    # File manager stack
+    # File manager stack. thunar and tumbler come from their modules above;
+    # ffmpegthumbnailer is what tumbler uses for video thumbnails.
     gvfs
     udisks2
     ntfs3g
+    ffmpegthumbnailer
 
     # Theming. Same derivations the greeter uses, see flake.nix.
     moonarchThemes.gtk