nix: add runner images outputs

nix/modules/ec-runner.nix

@@ -0,0 +1,28 @@
+{ lib, config, pkgs, self, ... }:
+
+let
+  cfg = config.services.every-channel.runner;
+in
+{
+  options.services.every-channel.runner = {
+    enable = lib.mkEnableOption "every.channel runner base system profile";
+  };
+
+  config = lib.mkIf cfg.enable {
+    # Minimal, conservative baseline for headless runners.
+    networking.useDHCP = lib.mkDefault true;
+    services.openssh.enable = lib.mkDefault true;
+
+    # Keep Nix flakes available on the runner itself.
+    nix.settings.experimental-features = lib.mkDefault [ "nix-command" "flakes" ];
+
+    # Provide the flake source tree at a stable path (symlink into /nix/store).
+    environment.etc."every-channel/flake".source = self;
+
+    environment.systemPackages = with pkgs; [
+      git
+      jq
+      curl
+    ];
+  };
+}