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/adv2_scenario_test.go

@@ -284,7 +284,8 @@ func TestAdv2Scenario_HarvestForestShadows(t *testing.T) {
 	// Seed harvest nodes for the entry room (they're auto-seeded by
 	// loadHarvestNodes on first read, but confirm we get at least one).
 	roomIdx := currentRoomIndexFor(exp)
-	nodes := loadHarvestNodes(exp, roomIdx)
+	nodeID := currentNodeIDFor(exp)
+	nodes := loadHarvestNodes(exp, nodeID)
 	t.Logf("room %d has %d harvest nodes", roomIdx, len(nodes))
 	if len(nodes) == 0 {
 		t.Error("expected at least one harvest node seeded")