feat(nix): nix and back again

I tried Nix, but it had too many downsides so I removed it.

1. Didn't like that all files are immutable and simple config changes
need a complete rebuild.
2. Setting up a new Mac didn't work as smoothly as promised. Not worth
the effort.
3. It sucked a lot to always have to type in the password twice on each
darwin-rebuild
4. It solves problems I never had.

.config/fish/functions/fe.fish

@@ -0,0 +1,10 @@
+# fe [FUZZY PATTERN] - Open the selected file with the default editor
+#   - Bypass fuzzy finder if there's only one match (--select-1)
+#   - Exit if there's no match (--exit-0)
+function fe --description "Open the selected file with the default editor"
+    set files (fzf-tmux --query=$argv --multi --select-1 --exit-0 | string split \n)
+
+    if test -n "$files"
+        $EDITOR $files; and true # This line is added to prevent failure when using "set -e" in shell.
+    end
+end