feat(nixos): deploy Gitea guest on Pikachu

configs/nixos/guests/gitea.nix

@@ -0,0 +1,40 @@
+{
+  config,
+  lib,
+  registry,
+  ...
+}:
+let
+  cfg = config.guests.gitea;
+in
+{
+  options.guests.gitea.dataPath = lib.mkOption {
+    type = lib.types.nullOr lib.types.str;
+    default = null;
+    example = "/srv/gitea";
+    description = "Host path mounted as Gitea's state directory.";
+  };
+
+  config = lib.mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = cfg.dataPath != null;
+        message = "guests.gitea.dataPath must point at the host directory that stores Gitea state.";
+      }
+    ];
+
+    guests.gitea = {
+      interior.modules.services.gitea = {
+        enable = true;
+        reverseProxyAddress = registry.address.${config.networking.hostName}."reverse-proxy";
+      };
+
+      mounts."/var/lib/gitea" = {
+        directory = cfg.dataPath;
+        owner = config.registry."stable-uid".${config.networking.hostName}.gitea;
+        group = "storage";
+        mode = "2770";
+      };
+    };
+  };
+}