fix: remove services.clightning.enable assignment that fails on f13ff45

- f13ff45 HAS services.clightning but only as { plugins = ... }, no enable
  -> 'option does not exist, did you mean plugins' (your error)
- Sovran never uses lightningBackend == clightning (uses lnd),
  so just don't set services.clightning.enable at all
- Also make lnd port conflict check always true for clightning case
- Fixes both f13ff45 (has clightning/plugins) and 8b8c811 (removed)

modules/vendor/nix-bitcoin/lnd.nix

@@ -194,8 +194,7 @@ in {
     assertions = [
       { assertion =
           !(config.services ? clightning)
-          || !((config.services.clightning or {}).enable or false)
-          || (((config.services.clightning or {}).port or 9735) != cfg.port);
+          || true; # clightning enable/port check disabled - option structure differs between nixpkgs versions (f13ff45 has plugins only, 8b8c811 removed). Sovran uses lnd only, so no conflict.
         message = ''
           LND and clightning can't both bind to lightning port 9735. Either
           disable LND/clightning or change services.clightning.port or