refactor(flake): move flake modules into separate subdirectories

Also put `outputs` before `inputs` in `flake.nix` (readability)

modules/flake/deploy/default.nix

@@ -0,0 +1,45 @@
+{ lib, config, self, inputs, ... }:
+
+let
+  inherit (config.lib)
+    accumulateHosts
+    configuration-type-to-deploy-type;
+in
+{
+  flake = {
+    deploy.nodes =
+      accumulateHosts
+        # TODO: nix-on-droid
+        ["nixos" "nix-darwin"]
+        ({ host, system, configuration-type, configuration }:
+          let
+            deploy-config-path =
+              "${config.flake.autoConfigurations.${configuration-type}.dir}/${system}/${host}/deploy.nix";
+            deploy-config =
+              import deploy-config-path;
+          in
+            lib.optionalAttrs
+              (builtins.pathExists deploy-config-path)
+              {
+                ${host} = {
+                  inherit (deploy-config)
+                  hostname;
+                  profiles.system = deploy-config // {
+                    path =
+                      let
+                        deploy-type = configuration-type-to-deploy-type configuration-type;
+                      in
+                        inputs.deploy-rs.lib.${system}.activate.${deploy-type} configuration;
+                  };
+                };
+              }
+        );
+
+    checks =
+      lib.mapAttrs
+        (system: deployLib:
+          deployLib.deployChecks
+            self.deploy)
+        inputs.deploy-rs.lib;
+  };
+}