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>

gogobee_branching_zones_plan.md

@@ -378,5 +378,6 @@ When the new session starts:
 3. Read `gogobee_dungeon_zones.md` (existing zone design) + `internal/plugin/dnd_zone.go` for current shape.
 4. Run G1 (schema) + G2 (types) + G3 (legacy compiler) + G4 (run state). All four are infra; ship together with no behavior change.
 5. Land G5 navigation behind `GOGOBEE_BRANCHING_ZONES=1` env gate.
-6. POC G7 with Crypt of Valdris.
-7. Pause for playtest before G8 mass migration.
+6. **G6 (done)** — dependent surfaces: harvest re-keyed on `node_id` (with legacy `room_idx` read-fallback + drop-on-save migration), narration cadence salted on `len(visited_nodes)-1` via `narrationCadence(run)`, `!zone map` graph render gated by `GOGOBEE_BRANCHING_ZONES=1` (locked edges → `╳`, secrets hidden until visited), and a region-boundary hook in graph advance/`!zone go` that mirrors `!region travel` flavor + log without burning supplies (graph is run-state authoritative).
+7. POC G7 with Crypt of Valdris.
+8. Pause for playtest before G8 mass migration.