Branching zones G6: dependent surfaces re-keyed on graph nodes

- Harvest tables (expedition + standalone) now keyed by node_id; legacy
  room-idx entries auto-migrate via read-fallback + drop-on-save.
- Narration salts swapped from run.CurrentRoom to narrationCadence(run)
  (= len(visited_nodes)-1) so flavor pickers survive G9 column drop.
- !zone map renders the graph (BFS by PosX/PosY) when the gate is on:
  ✓/▶/· status, ╳ for locked-only edges, secrets hidden until visited.
- Region-boundary hook in graph advance/!zone go updates expedition
  CurrentRegion + visited list when from/to nodes differ — without
  burning supplies or retiring runs (the graph IS the run state).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/plugin/dnd_zone_harvest_test.go

@@ -48,8 +48,9 @@ func TestStandaloneHarvest_RoutesToZoneRun(t *testing.T) {
 	if raw == "" || raw == "{}" {
 		t.Errorf("expected harvest_nodes_json populated after standalone harvest, got %q", raw)
 	}
-	if !strings.Contains(raw, "\"0\":") {
-		t.Errorf("expected room 0 entry in harvest table, got %q", raw)
+	wantKey := "\"" + deriveLegacyNodeID(run.ZoneID, 0) + "\":"
+	if !strings.Contains(raw, wantKey) {
+		t.Errorf("expected entry node %s in harvest table, got %q", wantKey, raw)
 	}
 }