Add Huarong retreat scenario

docs/DATA_MODEL.md

@@ -41,6 +41,7 @@ data/scenarios/027_jiangling_chase.json
 data/scenarios/028_xiakou_pursuit.json
 data/scenarios/029_red_cliffs_fleet.json
 data/scenarios/030_red_cliffs_fire.json
+data/scenarios/031_huarong_retreat.json
 ```
 
 ## Campaign
@@ -83,7 +84,8 @@ The campaign file defines scenario order, resource paths, and officers who are a
     { "id": "027_jiangling_chase", "title": "Jiangling Chase", "path": "res://data/scenarios/027_jiangling_chase.json" },
     { "id": "028_xiakou_pursuit", "title": "Xiakou Pursuit", "path": "res://data/scenarios/028_xiakou_pursuit.json" },
     { "id": "029_red_cliffs_fleet", "title": "Red Cliffs Fleet", "path": "res://data/scenarios/029_red_cliffs_fleet.json" },
-    { "id": "030_red_cliffs_fire", "title": "Red Cliffs Fire", "path": "res://data/scenarios/030_red_cliffs_fire.json" }
+    { "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" }
   ]
 }
 ```

docs/ROADMAP.md

@@ -21,7 +21,7 @@
 - Destination victory conditions and objective map markers exist.
 - Turn-limit conditions and HUD turn-limit display exist.
 - Victory reward summary is visible.
-- Next-battle flow exists across the current thirty-scenario campaign.
+- Next-battle flow exists across the current thirty-one-scenario campaign.
 - Campaign completion and new-campaign reset exist.
 - Reward inventory can be brought into the next battle.
 
@@ -52,7 +52,7 @@
 - Party roster persistence has a first save-file skeleton.
 - Level, experience, and equipment persistence.
 - Chapter selection and save/load.
-- Linear thirty-scenario campaign order exists.
+- Linear thirty-one-scenario campaign order exists.
 - Save reset exists.
 - Victory rewards, consumable counts, equipment stock, and equipped gear persist.
 - A basic pre-battle shop with scenario-specific stock exists. Sell-back and richer item management are still planned.
@@ -90,6 +90,7 @@
 - Twenty-eighth-scenario content exists with Xiakou pursuit, river harbor pressure, Sun-Liu coalition hints, and 027 branch reactions.
 - Twenty-ninth-scenario content exists with Red Cliffs fleet pressure, chained ships, coalition vanguard, and 028 branch reactions.
 - Thirtieth-scenario content exists with Red Cliffs fire ships, chained-fleet danger, coalition fire tactics, and 029 branch reactions.
+- Thirty-first-scenario content exists with Huarong retreat pressure, coalition roadblocks, Cao Cao's escape route, and 030 branch reactions.
 
 ## Milestone 5: Presentation