Long expeditions D1-a: graph-driven TotalRooms; goblin_warrens 7→16

Length is now sourced from the zone graph's longest entry→boss path,
not the dice roll, so "Room X/Y" matches what the player walks. The
dice fallback stays for graphless zones.

Goblin Warrens grows to the T1 12–14 band (13-node traversal): adds the
missing Trap anchor and deepens both fork branches + the post-merge
approach. Pattern reference for the remaining zones in D1-b…d.

internal/plugin/dnd_zone_run.go

@@ -108,11 +108,21 @@ func (r *DungeonRun) CurrentRoomType() RoomType {
 // generateRoomSequence builds the deterministic-but-seeded room layout
 // for a run of the given zone. The boss room is always last; one Entry
 // is always first; one Trap and one Elite room sit between explorations.
-// Total length is sampled in [zone.MinRooms, zone.MaxRooms].
+//
+// Total length tracks the zone's *graph* longest entry→boss path so the
+// "Room X/Y" display lines up with what the player actually walks. If
+// the graph hasn't been authored / can't be loaded, we fall back to a
+// dice roll within [zone.MinRooms, zone.MaxRooms] (the pre-graph shape).
 func generateRoomSequence(zone ZoneDefinition, rng *rand.Rand) []RoomType {
-	total := zone.MinRooms
-	if zone.MaxRooms > zone.MinRooms {
-		total += rng.IntN(zone.MaxRooms - zone.MinRooms + 1)
+	total := 0
+	if g, ok := loadZoneGraph(zone.ID); ok {
+		total = graphLongestPath(g)
+	}
+	if total == 0 {
+		total = zone.MinRooms
+		if zone.MaxRooms > zone.MinRooms {
+			total += rng.IntN(zone.MaxRooms - zone.MinRooms + 1)
+		}
 	}
 	// Fixed slots: Entry + Trap + Elite + Boss = 4. Remaining = explorations.
 	const fixed = 4