nix: move dev outputs to subflake

nix/dev/shell.nix

@@ -0,0 +1,36 @@
+{
+  perSystem = {
+    pkgs,
+    config,
+    self',
+    refraction',
+    ...
+  }: {
+    devShells.default = pkgs.mkShell {
+      shellHook = ''
+        ${config.pre-commit.installationScript}
+      '';
+
+      packages = with pkgs; [
+        # general
+        actionlint
+        nodePackages.prettier
+        config.procfiles.daemons.package
+
+        # rust
+        clippy
+        rustfmt
+        rust-analyzer
+
+        # nix
+        self'.formatter
+        deadnix
+        nil
+        statix
+      ];
+
+      inputsFrom = [refraction'.packages.refraction];
+      RUST_SRC_PATH = "${pkgs.rustPlatform.rustLibSrc}";
+    };
+  };
+}