Add Xiakou pursuit 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-seven-scenario campaign.
+- Next-battle flow exists across the current twenty-eight-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-seven-scenario campaign order exists.
+- Linear twenty-eight-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.
@@ -87,6 +87,7 @@
 - Twenty-fifth-scenario content exists with Xinye advance, Liu Bei's rearguard, Jing Province pressure, and 024 branch reactions.
 - Twenty-sixth-scenario content exists with Changban pursuit, Liu Bei's bridge guard, Zhang Fei pressure, and 025 branch reactions.
 - Twenty-seventh-scenario content exists with Jiangling chase, Jing Province storehouses, Liu Bei's retreat, and 026 branch reactions.
+- Twenty-eighth-scenario content exists with Xiakou pursuit, river harbor pressure, Sun-Liu coalition hints, and 027 branch reactions.
 
 ## Milestone 5: Presentation