(feat) Update dotfile scripts & tooling

- Update & split scripts
- Main package install script
- Fish / environment install script
- Dockerfile for testing locally

fish/config.fish

@@ -1,7 +1,8 @@
-set -Ux PYENV_ROOT $HOME/.pyenv
-set -Ux fish_user_paths $PYENV_ROOT/bin $fish_user_paths
+if status is-interactive
+    # Commands to run in interactive sessions can go here
 
-# pyenv init
-if command -v pyenv 1>/dev/null 2>&1
-    pyenv init - | source
+    # pyenv init
+    if command -v pyenv 1>/dev/null 2>&1
+        pyenv init - | source
+    end
 end