feat(fzf): configure and integrate into shells

configs/fzf.nix

@@ -0,0 +1,36 @@
+{ pkgs, lib, ... }:
+{
+  environment = {
+    systemPackages = [ pkgs.fzf ];
+    variables = {
+      FZF_DEFAULT_OPTS = lib.escapeShellArgs [
+        "--height 40%"
+        "--layout=reverse"
+      ];
+      FZF_ALT_C_COMMAND = "${pkgs.fd}/bin/fd --type d";
+      FZF_ALT_C_OPTS = lib.escapeShellArgs [
+        "--preview '${pkgs.tree}/bin/tree -L 1 {}'"
+        "--bind='space:toggle-preview'"
+        "--preview-window=hidden"
+      ];
+      FZF_CTRL_T_COMMAND = "${pkgs.fd}/bin/fd --type f";
+      FZF_CTRL_T_OPTS = lib.escapeShellArgs [
+        "--preview '${pkgs.bat}/bin/bat {}'"
+      ];
+    };
+  };
+
+  programs.zsh.interactiveShellInit = ''
+    if [[ $options[zle] = on ]]; then
+      . ${pkgs.fzf}/share/fzf/completion.zsh
+      . ${pkgs.fzf}/share/fzf/key-bindings.zsh
+    fi
+  '';
+
+  programs.bash.interactiveShellInit = ''
+    if [[ :$SHELLOPTS: =~ :(vi|emacs): ]]; then
+      . ${pkgs.fzf}/share/fzf/completion.bash
+      . ${pkgs.fzf}/share/fzf/key-bindings.bash
+    fi
+  '';
+}