feat(darwin)!: update config

Add `nix` initialization script to shell's `extraConfig`
  - fixes `nix` when updating MacOS
Add `flameshot` to `brew` packages
Fix tilde (`~`) remapping
  - mysteriously switched after a restart, needed to swap
Add (noncompiling) `borders` (`JankyBorders`) config
Add `TODO` to `sketchybar` config

modules/nix-darwin/yabai/skhdrc

@@ -98,6 +98,9 @@ shift + cmd - space : \
     yabai -m window --toggle border; \
     sketchybar --trigger window_focus
 
+# Prepare (next spawned window) to swallow parent
+alt - s : yabai -m window --insert stack
+
 # Restart Yabai
 shift + lctrl + alt - r : \
     /usr/bin/env osascript <<< \