refactor(flake)!: export packages using a flake module

Also stop passing `outputs` around, prefer `inputs.self`
Also put all `auto_` in `readOnly` `internal` options
- `autoModules`, `autoConfigurations` and `autoPackages`
Do not export packages as overlay (causes an infinite recursion)
- this is documented on the two places it has effect on
-- in `./overlays/default.nix` and `./modules/flake/configurations.nix`
-- in `autoConfigurations` we manually extend `pkgs` with the flake packages
Allow packages to say what `systems` they are compatible with
- See `./pkgs/swww/systems.nix` - disabled for all systems
- See `./pkgs/pngpaste/systems.nix` - enabled only for `darwin` targets

hosts/nix-on-droid/aarch64-linux/cheetah/configuration.nix

@@ -1,4 +1,4 @@
-{ inputs, outputs, lib, pkgs, config, ... }:
+{ inputs, lib, pkgs, config, ... }:
 
 {
   environment.packages = with pkgs; [ ];

hosts/nix-on-droid/aarch64-linux/cheetah/home.nix

@@ -1,4 +1,4 @@
-{ inputs, outputs, lib, pkgs, config, ... }:
+{ inputs, lib, pkgs, config, ... }:
 
 {
   # Home Manager needs a bit of information about you and the