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.go

@@ -214,8 +214,8 @@ func zoneGoblinWarrens() ZoneDefinition {
 		Faction:    "Goblins, Hobgoblins",
 		Atmosphere: "Low ceilings, torchlight, crude traps, cackling in the dark.",
 		Hook:       "A network of fetid tunnels burrowed beneath the Merchant's Road. The smell arrives before the sounds — smoke, rot, and something worse. I advise keeping one hand on your blade.",
-		MinRooms:   6,
-		MaxRooms:   7,
+		MinRooms:   12,
+		MaxRooms:   14,
 		Enemies: []ZoneEnemy{
 			{BestiaryID: "goblin_sneak", SpawnWeight: 7},
 			{BestiaryID: "goblin_archer", SpawnWeight: 6},