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_narration.go

@@ -330,6 +330,22 @@ func eliteRoomEntryLine(zoneID ZoneID, runID string, roomIdx int) string {
 	return "🎭 **TwinBee:** " + line
 }
 
+// narrationCadence returns the salt index used to seed narration
+// pickers — the count of nodes visited so far (0-based, matching the
+// pre-G6 CurrentRoom semantics). Both linear-mode and graph-mode
+// advance bump len(VisitedNodes) in lockstep with CurrentRoom, so this
+// preserves existing pick determinism while letting G9 drop the legacy
+// current_room column without re-keying every flavor pool seed.
+func narrationCadence(run *DungeonRun) int {
+	if run == nil {
+		return 0
+	}
+	if n := len(run.VisitedNodes); n > 0 {
+		return n - 1
+	}
+	return run.CurrentRoom
+}
+
 // pickLineDeterministic — stable selection across (runID, salt). Same
 // inputs always yield the same line, so a player who re-reads status
 // sees the same prose; different rooms / different runs vary.