Add Bohai remnants scenario

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 twenty-scenario campaign.
+- Next-battle flow exists across the current twenty-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 twenty-scenario campaign order exists.
+- Linear twenty-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.
@@ -80,6 +80,7 @@
 - Eighteenth-scenario content exists with Northern Pursuit, Yuan Shang's rearguard, and 017 branch reactions.
 - Nineteenth-scenario content exists with Nanpi pressure, Yuan Tan's outer defense, and 018 branch reactions.
 - Twentieth-scenario content exists with Nanpi surrender, Yuan Tan loyalists, and 019 branch reactions.
+- Twenty-first-scenario content exists with Bohai remnants, Yuan brothers' covering force, and 020 branch reactions.
 
 ## Milestone 5: Presentation