ci: drop darwin shims, rebuild locally on netty runner

- remove macOS-era `sudo mkdir /Users/rathi/...` shim steps from flake-check
  and nix-format (Linux runner, paths don't exist, gitea-runner has no sudo)
- deploy-netty now runs `sudo nixos-rebuild switch --flake .#netty` directly
  on the runner (it *is* netty), no SSH, no `just switch-netty`
- grant gitea-runner NOPASSWD sudo for nixos-rebuild only
- apply current nixfmt to home/scripts.nix, hermes-gateway.nix, devshells.nix

Made-with: Cursor

modules/devshells.nix

@@ -9,13 +9,12 @@
     {
       formatter = pkgs.nixfmt-tree;
 
-      packages =
-        {
-          home-manager = inputs.home-manager.packages.${system}.home-manager;
-        }
-        // lib.optionalAttrs (lib.hasSuffix "darwin" system) {
-          darwin-rebuild = inputs.nix-darwin.packages.${system}.darwin-rebuild;
-        };
+      packages = {
+        home-manager = inputs.home-manager.packages.${system}.home-manager;
+      }
+      // lib.optionalAttrs (lib.hasSuffix "darwin" system) {
+        darwin-rebuild = inputs.nix-darwin.packages.${system}.darwin-rebuild;
+      };
 
       devShells.default = pkgs.mkShell {
         packages = with pkgs; [