feat(desktop): P28 民居第二变体强化配色与轮廓（青灰挑檐色阶 + 竖长格栅窗 + 绿院门）

- make-jiangnan-art.py slot 28/29/30：B 变体改用亮青灰瓦色阶、竖长木格栅窗、绿双扇院门
- VillageArt 变体 B 渲染：挑檐多叠一层、向两侧各出一格（水面之上不叠），墙身统一格栅窗
- 仅绘制分支，瓦片/可达性零改动

2 files changed, 16 insertions, 7 deletions

diff --git a/src/LivingVillage.Desktop/Assets/jiangnan-world.png b/src/LivingVillage.Desktop/Assets/jiangnan-world.png
index 11145a8..b67dd01 100644
--- a/src/LivingVillage.Desktop/Assets/jiangnan-world.png
+++ b/src/LivingVillage.Desktop/Assets/jiangnan-world.png
diff --git a/src/LivingVillage.Desktop/VillageArt.fs b/src/LivingVillage.Desktop/VillageArt.fs
index d2fcc1a..9a56de4 100644
--- a/src/LivingVillage.Desktop/VillageArt.fs
+++ b/src/LivingVillage.Desktop/VillageArt.fs
@@ -612,7 +612,8 @@ module VillageArt =
         spriteBatch.Draw(pixel, XnaRectangle(x, y, max 1 w, max 1 h), color)
 
     /// P26 民居立面变体：按位置确定性交替两种立面（沿河沿路分布）。
-    /// 0 = 黛瓦脊 + 木墙/窗 + 门（P24 原样）；1 = 挑檐挑出 + 木格栅窗 + 院门。
+    /// 0 = 黛瓦脊 + 木墙/窗 + 门（P24 原样）；1 = 亮青灰挑檐（多叠一层、向两侧各出一格）+
+    /// 竖长木格栅窗 + 绿院门（P28 强化配色与轮廓，保证 512 整图 ~2px/tile 下两变体可分）。
     /// 纯函数、不改变任何瓦片/可达性语义；64x48 与 256x192 的 tiles checksum 不受影响。
     let houseFacadeVariant (building: MapGen.Building) : int =
         let remainder = (building.Left + building.Top) % 2
@@ -649,14 +650,22 @@ module VillageArt =
                         else WallWoodSprite
                     drawCell wallSprite x building.DoorY
             | _ ->
-                // 变体 B（P26）：挑檐向两侧各出一格 + 木格栅窗 + 院门。
-                for x in (left - 1) .. (right + 1) do
-                    drawCell RoofEaveOverhangSprite x building.Top
+                // 变体 B（P26/P28）：亮青灰挑檐向两侧各出一格 + 竖长木格栅窗 + 绿院门。
+                // P28 再向上叠一层挑檐，使 B 的轮廓比 A 高一格；水面之上不叠，避免屋顶压水。
+                let isWater x y =
+                    x >= 0 && x < map.Width && y >= 0 && y < map.Height
+                    && map.Tiles.[y * map.Width + x] = int MapGen.GroundTile.Water
+                for row in building.Top .. building.DoorY - 1 do
+                    for x in (left - 1) .. (right + 1) do
+                        drawCell RoofEaveOverhangSprite x row
+                let upper = building.Top - 1
+                if upper >= 0 then
+                    for x in (left - 1) .. (right + 1) do
+                        if not (isWater x upper) then
+                            drawCell RoofEaveOverhangSprite x upper
                 for x in left .. right do
                     let wallSprite =
-                        if x = building.DoorX then CourtyardDoorSprite
-                        elif (x - left) % 2 = 0 then WallLatticeSprite
-                        else WallWoodSprite
+                        if x = building.DoorX then CourtyardDoorSprite else WallLatticeSprite
                     drawCell wallSprite x building.DoorY
         // P26 河岸装饰：护岸石垒 / 芦苇 / 垂柳（垂柳占上下两格），只在大图生成。
         for decoration in map.Decorations do