manatee: add self-hosted todo app

Wire the offline-first todo app (github: local /home/alex/code/todo) into
manatee, following the app-module convention:

- flake input `todo` (local git checkout for now; gitea URL commented) with
  nixpkgs following.
- hosts/manatee/modules/todo: mod.todo option importing the app's NixOS module;
  runs on 127.0.0.1:8091, secureCookies, token from agenix; the host owns the
  nginx vhost (todo.ppp.pm, forceSSL + useACMEHost) and homepage card.
- mod.todo.enable = true.
- certs: todo.ppp.pm DNS-01 cert via hetzner.
- home-assistant DNS updater: add `todo` to the Hetzner subdomain list.
- secrets: todo-token.age (encrypted access token) + recipients in secrets.nix.

hosts/manatee/modules/certs/default.nix

@@ -59,6 +59,19 @@
           "--http-timeout=60"
         ];
       };
+
+      "todo.ppp.pm" = {
+        dnsProvider = "hetzner";
+        environmentFile = config.age.secrets.hetzner-dns.path;
+        group = "nginx";
+
+        extraLegoFlags = [
+          "--dns.resolvers=1.1.1.1:53,8.8.8.8:53"
+          "--dns.propagation-wait=60s"
+          "--dns-timeout=60"
+          "--http-timeout=60"
+        ];
+      };
     };
   };