nixos/fzf: fix bash with fuzzyCompletion

put all of fzf initialization after the bash-completions initialization
in bashrc, as the upstream project suggests in
https://github.com/junegunn/fzf/issues/72

Fixes: #303195

nixos/modules/programs/fzf.nix

@@ -15,11 +15,12 @@ in
     environment.systemPackages = lib.mkIf (cfg.keybindings || cfg.fuzzyCompletion) [ pkgs.fzf ];
 
     programs = {
-      bash.interactiveShellInit = lib.optionalString cfg.fuzzyCompletion ''
+      # load after programs.bash.enableCompletion
+      bash.promptPluginInit = lib.mkAfter (lib.optionalString cfg.fuzzyCompletion ''
         source ${pkgs.fzf}/share/fzf/completion.bash
       '' + lib.optionalString cfg.keybindings ''
         source ${pkgs.fzf}/share/fzf/key-bindings.bash
-      '';
+      '');
 
       zsh = {
         interactiveShellInit = lib.optionalString (!config.programs.zsh.ohMyZsh.enable)