Add Forgejo runner to CI host config

hosts/ci/configuration.nix

@@ -4,5 +4,7 @@
     ../../shared/base.nix
     ../../shared/hardware/vm.nix
     ../../shared/disko/basic-ext4.nix
+
+    ../../servers/ci.nix
   ];
 }

servers/ci.nix

@@ -0,0 +1,26 @@
+{ pkgs, ... }:
+{
+  networking.firewall.trustedInterfaces = [ "br-+" ];
+
+  services.gitea-actions-runner = {
+    package = pkgs.forgejo-runner;
+    instances."forgejo.sinerva.eu" = {
+      enable = true;
+      name = "ci-forgejo-runner";
+      tokenFile = "/persist/secrets/forgejo_token";
+      url = "https://code.forgejo.org/";
+      labels = [
+        "Ubuntu-24.04-LTS:docker://ubuntu:24.04"
+        "nixos-latest:docker://nixos/nix"
+      ];
+    };
+  };
+
+  virtualisation.docker = {
+    enable = true;
+    daemon.settings = {
+      fixed-cidr-v6 = "fd00::/80";
+      ipv6 = true;
+    };
+  };
+}