feat(p41): 夜帧船篷对比暗化

- VillageArt.drawCc0BoatOverlay 增加夜层专用暗化系数 0.7（仅夜光晕层生效，
  白天不调用 overlay，p40-day/p40-boat 逐字节不变）
- P40ArtTests 新增 NightBoatAwningIsAtLeast40GreyDarkerThanSurroundingGlow：
  内嵌 PNG 解码读取夜帧，断言船 2 瓦包围盒比 24px 光晕环至少暗 40 灰阶
- 新增 scripts/check-p40-night-boat-contrast.py 独立像素守卫
- 重出 docs/evidence/p40-night.png（contrast 103.2 >= 40）

1 files changed, 10 insertions, 2 deletions

diff --git a/src/LivingVillage.Desktop/VillageArt.fs b/src/LivingVillage.Desktop/VillageArt.fs
index 2b2b0e7..0f176aa 100644
--- a/src/LivingVillage.Desktop/VillageArt.fs
+++ b/src/LivingVillage.Desktop/VillageArt.fs
@@ -970,18 +970,26 @@ module VillageArt =
                 for (rect, color) in lanternGlowLayers centerX centerY radiusPixels 8 255 214 150 peakAlpha do
                     spriteBatch.Draw(pixel, rect, color)
 
+    let cc0BoatNightTintScale = 0.7f
+
     let drawCc0BoatOverlay
         (spriteBatch: SpriteBatch)
         (textures: ArtTextures)
         (camera: XnaVector2)
         (map: MapGen.Result)
         (tint: XnaColor) =
+        let night =
+            XnaColor(
+                int (float32 tint.R * cc0BoatNightTintScale),
+                int (float32 tint.G * cc0BoatNightTintScale),
+                int (float32 tint.B * cc0BoatNightTintScale),
+                int tint.A)
         match textures.Cc0TileAtlas with
         | Some cc0 ->
             match cc0BoatTile map with
             | Some (boatX, boatY) ->
-                drawCc0Tile spriteBatch cc0 tint (cc0TileRect cc0TileIndexBoatLeft) (boatX * Sim.tilePixels - int camera.X) (boatY * Sim.tilePixels - int camera.Y)
-                drawCc0Tile spriteBatch cc0 tint (cc0TileRect cc0TileIndexBoatRight) ((boatX + 1) * Sim.tilePixels - int camera.X) (boatY * Sim.tilePixels - int camera.Y)
+                drawCc0Tile spriteBatch cc0 night (cc0TileRect cc0TileIndexBoatLeft) (boatX * Sim.tilePixels - int camera.X) (boatY * Sim.tilePixels - int camera.Y)
+                drawCc0Tile spriteBatch cc0 night (cc0TileRect cc0TileIndexBoatRight) ((boatX + 1) * Sim.tilePixels - int camera.X) (boatY * Sim.tilePixels - int camera.Y)
             | None -> ()
         | None -> ()