treewide: yet another restructure

modules, overlays, and packages have their own default.nix re-exporting
things instead of reading file paths. slightly improves declarativeness.

wine-osu is removed; we're just using nix-gaming (for now).

our custom packages will now have to be accessed via pkgs.me instead of
just pkgs. helps know where it came from

future goals: get rid of our overlays completely, or at least not make
it replace anything from nixpkgs

modules/system/base.nix

@@ -20,7 +20,6 @@
   };
   nix.registry.config.flake = inputs.self;
   nix.registry.nixpkgs.flake = inputs.nixpkgs;
-  nixpkgs.overlays = overlays;
 
   home-manager = {
     useGlobalPkgs = true;