Add Huarong retreat scenario

data/campaign/campaign.json

@@ -153,6 +153,11 @@
       "id": "030_red_cliffs_fire",
       "title": "Red Cliffs Fire",
       "path": "res://data/scenarios/030_red_cliffs_fire.json"
+    },
+    {
+      "id": "031_huarong_retreat",
+      "title": "Huarong Retreat",
+      "path": "res://data/scenarios/031_huarong_retreat.json"
     }
   ]
 }