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

hosts/netty/hermes-gateway.nix

@@ -63,7 +63,7 @@ in
       };
     };
 
-    mcpServers = {};
+    mcpServers = { };
 
     extraPackages = with pkgs; [
       nodejs_22