Staged undo, built-ins window, machine warnings; raw and dynamic set fixes

- Undo is staged like any edit: in review mode the web UI's Undo, and hc
  history undo with -C or HOUSECARL_CHANGESET, add a revert operation
  that checks, when replayed, that nothing it touches changed since;
  applied, History links the entries. Imports and takeovers still can't
  be staged.
- The rules page sums up a chain's built-ins in one line; a window lists
  them with what they do and their hits, and switches them.
- Warnings about the machine (dashboard, hc status): nftables.service
  enabled (it loads /etc/nftables.conf at boot and flushes every table
  when stopped), and the imported table still in force beside
  Housecarl's. The docs say to disable nftables.service but not stop it.
- A raw rule with other fields set is refused (raw_conflict) instead of
  silently ignoring them; the rule dialog's nftables section hides what
  it replaces, and the importer's raw rules carry only their text.
- A dynamic set with configured entries is refused
  (set_dynamic_entries): they were silently ignored. The set dialog
  shows entries or the entry timeout, as fits.
- The rule dialog's chain choices are just the chains' names.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/server/h_config.go

@@ -469,13 +469,27 @@ func (s *Server) revertHistory(w http.ResponseWriter, r *http.Request, p *auth.P
 	if err := require(p, auth.ResConfig, true); err != nil {
 		return err
 	}
-	if err := notStaged(r, "an undo"); err != nil {
-		return err
-	}
 	id, err := pathID(r, "id")
 	if err != nil {
 		return err
 	}
+	// Staged, an undo is an operation of its own, reviewed like any.
+	if csID, err := changesetParam(r); err != nil {
+		return err
+	} else if csID != 0 {
+		h, err := s.store.GetHistory(r.Context(), id)
+		if errors.Is(err, store.ErrNotFound) {
+			return notFound("history entry %d not found", id)
+		}
+		if err != nil {
+			return err
+		}
+		if h.RevertedBy != 0 {
+			return conflict("history entry %d was already undone by entry %d", id, h.RevertedBy)
+		}
+		data, _ := json.Marshal(h)
+		return s.stage(w, r, p, csID, model.Op{Op: model.OpRevert, ID: id, Data: data})
+	}
 	res, err := s.eng.Revert(r.Context(), p, id, engine.Options{DryRun: queryBool(r, "dry_run"), Via: via(r, p)})
 	if err != nil {
 		s.writeErr(w, r, err, res)