refactor: Use haumea for filesystem-based module system for flake outputs

refactor: Use hyphen(`-`) for variable names & folder names(except Python), replace all unserscore(`_`) with hyphen(`-`).

home/linux/base/shell.nix

@@ -1,13 +1,13 @@
 {
   config,
-  username,
+  myvars,
   ...
 }: let
   d = config.xdg.dataHome;
   c = config.xdg.configHome;
   cache = config.xdg.cacheHome;
 in rec {
-  home.homeDirectory = "/home/${username}";
+  home.homeDirectory = "/home/${myvars.username}";
 
   # environment variables that always set at login
   home.sessionVariables = {