manatee: Add services homepage with auto-discovery

Add a homepage module that generates a static landing page served on
port 9999 via nginx. Each service module registers itself via the shared
mod.homepage.services option, so enabling a module automatically adds
it to the page.

hosts/manatee/modules/jellyfin/default.nix

@@ -47,6 +47,12 @@ in
       };
     };
 
+    mod.homepage.services = [{
+      name = "Jellyfin";
+      port = 8096;
+      description = "Media streaming";
+    }];
+
     networking = {
       firewall.allowedTCPPorts = [ 8096 ];
     };