refactor: reorganize server modules

- Moved each individual service definition into a dedicated `services/`
  directory under every server module (e.g.
`modules/servers/bragi/services/`).
- Updated the corresponding `default.nix` files to import the renamed
  service modules from the new location.
- Applied the same changes across all server modules, ensuring
  the API and import paths remain consistent.

modules/servers/heimdall/ntfy-sh.nix

@@ -1,33 +0,0 @@
-{...}: {
-  services.ntfy-sh = {
-    enable = true;
-    settings = {
-      base-url = "https://ntfy.cronyakatsuki.xyz";
-      listen-http = "127.0.0.1:2586";
-      behind-proxy = true;
-      auth-default-access = "deny-all";
-    };
-  };
-
-  services.traefik.dynamicConfigOptions.http = {
-    services.ntfy-sh.loadBalancer.servers = [
-      {
-        url = "http://localhost:2586";
-      }
-    ];
-
-    routers.ntfy-sh = {
-      rule = "Host(`ntfy.cronyakatsuki.xyz`)";
-      tls = {
-        certResolver = "porkbun";
-      };
-      service = "ntfy-sh";
-      entrypoints = "websecure";
-    };
-  };
-
-  services.restic.backups = {
-    local.paths = ["/var/lib/ntfy-sh"];
-    server.paths = ["/var/lib/ntfy-sh"];
-  };
-}