feat(nix): bootstrap clan-core for sunken-ship + phantom-ship 🏴‍☠️

Stage 4a of the dendritic + clan migration. Both servers now live under
clan.machines (via nixos/flake-modules/clan.nix) and clan-core generates
their nixosConfigurations for us; the previous per-host flake-modules
are removed.

Notes:
- clan.core.enableRecommendedDefaults = false on both machines so we
  keep the existing dhcpcd / non-networkd / non-resolved stack. Services
  like dnsmasq, navidrome, and the existing wireless setup break with
  the clan defaults on.
- dotfiles-rebuild timer is untouched (safety net). Replacing it with
  clan machines update / dm-pull-deploy comes in 4e.
- mac stays outside the clan as admin only.

Verified: `clan machines list --flake path:…/nixos` returns both hosts;
both servers rebuild cleanly and all services (navidrome, cloudflare-
tunnel, fitness-bot, dnsmasq, openclaw-gateway, sshd) stay active.

nixos/flake-modules/clan.nix

@@ -0,0 +1,55 @@
+# clan.lol wiring for the homelab.
+#
+# Declares `sunken-ship` and `phantom-ship` as clan machines. Each machine's
+# `imports` list is the NixOS module set that used to live in its own
+# flake-module. clan-core produces `flake.nixosConfigurations.<name>` from
+# these, which is why the old per-host flake-modules were removed.
+#
+# The mac stays outside the clan — admin only, uses `clan machines update`
+# to push to the servers.
+{ config, inputs, ... }:
+let
+  lib = inputs.nixpkgs.lib;
+  hmModule = { user, homeDirectory, stateVersion ? null, userImports ? [ ] }:
+    import ../lib/home-manager-user.nix {
+      inherit lib user homeDirectory stateVersion userImports;
+    };
+in {
+  imports = [ inputs.clan-core.flakeModules.default ];
+
+  clan = {
+    meta.name = "homelab";
+
+    # Preserve current network / init stack (no systemd-networkd/resolved,
+    # no boot.initrd.systemd, no extra debug packages). Revisit per-service
+    # in later stages rather than flipping this fleet-wide.
+    machines.sunken-ship = {
+      imports = [
+        { clan.core.enableRecommendedDefaults = false; }
+        ../hosts/sunken-ship.nix
+        config.flake.nixosModules.dotfiles-rebuild
+        inputs.home-manager.nixosModules.home-manager
+        (hmModule {
+          user = "danny";
+          homeDirectory = "/home/danny";
+          stateVersion = "25.11";
+        })
+      ];
+    };
+
+    machines.phantom-ship = {
+      imports = [
+        { clan.core.enableRecommendedDefaults = false; }
+        inputs.nix-openclaw.nixosModules.openclaw-gateway
+        ../hosts/phantom-ship.nix
+        config.flake.nixosModules.dotfiles-rebuild
+        inputs.home-manager.nixosModules.home-manager
+        (hmModule {
+          user = "danny";
+          homeDirectory = "/home/danny";
+          stateVersion = "25.11";
+        })
+      ];
+    };
+  };
+}