refactor: replace redundant mkForce with plain values and mkDefault

Each of these overrode a value nothing else set at a higher priority:

- qemu-guest: btrbk, hardwareTools and cloud-init have no competing
  definition on the guests.
- mdns: nixpkgs' sunshine module sets avahi.publish.* with mkDefault.
- computer-use: i18n now sets the time zone with mkDefault.
- darwin terminal: the shared ghostty/kitty font sizes are now mkDefault.
- shoukei: sunshine is mkDefault false in remote-desktop.nix, zram's
  memoryPercent is mkDefault 50; supportedFilesystems now merges instead
  of discarding the fsType entries other modules add.
- youko: nothing enables docker.
- nixpak: pasta.enable and sockets.pipewire are mkDefault in the shared
  modules, sockets.pulse already was.

Every NixOS host's toplevel drvPath is unchanged; on fern and frieren the
terminal font sizes and time zone evaluate to the same values.

Assisted-by: Claude Code (claude-opus-5-5)

hardening/nixpaks/modules/desktop-base.nix

@@ -45,7 +45,7 @@
       wayland = true;
       x11 = lib.mkDefault false;
       pulse = lib.mkDefault true;
-      pipewire = false;
+      pipewire = lib.mkDefault false;
     };
     bind.rw = with sloth; [
       [