feat(art): P33 接入 CC0 真实像素素材样板（地面+角色竖直切片）

- 修复 make-cc0-art.py 地块取样间距：packed sheet 无间距(16px pitch)，旧 17px 误采错格
- 重选草地/石板格 (9,8)/(10,8)/(4,8)/(4,9)，整数 2x NEAREST 重建 cc0-tiles.png
- VillageArt 暴露 selectedGround/CharacterAtlasRelativePath 纯函数，保留 LV_ASSET_PACK=cc0
  开关与程序绘制江南图集 fallback
- 新增 AssetPackTests：图集加载尺寸、整数倍缩放、开关/回退断言
- docs/素材来源.md 记录来源/许可/sha256/构建/开关；同步 assets-and-licenses 与维护说明 P33 小节
- docs/evidence/p33-atlas-*.png 昼/夜/2x 特写/程序绘制对照（check-no-white-blocks 0 命中）

2 files changed, 30 insertions, 6 deletions

diff --git a/src/LivingVillage.Desktop/Assets/cc0-tiles.png b/src/LivingVillage.Desktop/Assets/cc0-tiles.png
index 1e43bc8..204eba2 100644
--- a/src/LivingVillage.Desktop/Assets/cc0-tiles.png
+++ b/src/LivingVillage.Desktop/Assets/cc0-tiles.png
diff --git a/src/LivingVillage.Desktop/VillageArt.fs b/src/LivingVillage.Desktop/VillageArt.fs
index 4faa886..9a034aa 100644
--- a/src/LivingVillage.Desktop/VillageArt.fs
+++ b/src/LivingVillage.Desktop/VillageArt.fs
@@ -544,22 +544,46 @@ module VillageArt =
         else
             texture
 
+    /// Fallback switch for the real-pixel asset pack (P33 vertical slice). When
+    /// `LV_ASSET_PACK=cc0`, the sample village swaps its ground + villager atlases for
+    /// the provenanced CC0 packs; any other value keeps the procedural Jiangnan atlases.
     let useCc0Pack () : bool =
         System.Environment.GetEnvironmentVariable("LV_ASSET_PACK") = "cc0"
 
     let cc0TileAtlasRelativePath = "Assets/cc0-tiles.png"
+    // Source ground tiles are 16x16, upscaled exactly 2x to one Sim.tilePixels cell.
+    let cc0TileSourcePixels = 16
     let cc0TileAtlasWidth = Sim.tilePixels * 4
+    let cc0TileAtlasHeight = Sim.tilePixels
     let cc0CharacterAtlasRelativePath = "Assets/cc0-characters.png"
+    // Source Puny band is 16x24, upscaled exactly 2x to a 32x48 cell; atlas packs
+    // 5 variants x 4 directions x 6 frames.
+    let cc0CharacterSourceWidth = 16
+    let cc0CharacterSourceHeight = 24
+    let cc0CharacterCellWidth = 32
+    let cc0CharacterCellHeight = 48
+    let cc0CharacterVariantCount = 5
+    let cc0CharacterDirectionCount = 4
+    let cc0CharacterFrameCount = 6
+    let cc0CharacterAtlasWidth =
+        cc0CharacterCellWidth * cc0CharacterVariantCount * cc0CharacterDirectionCount * cc0CharacterFrameCount
+
+    /// Ground atlas selection: `Some cc0-tiles.png` when the pack is on, else `None`
+    /// so the renderer keeps its procedural Jiangnan ground as the fallback.
+    let selectedGroundAtlasRelativePath () : string option =
+        if useCc0Pack () then Some cc0TileAtlasRelativePath else None
+
+    /// Character atlas selection: real CC0 Puny sprites when the pack is on, else the
+    /// procedural Jiangnan character atlas (fallback).
+    let selectedCharacterAtlasRelativePath () : string =
+        if useCc0Pack () then cc0CharacterAtlasRelativePath else characterAtlasRelativePath
 
     let loadTextures (device: GraphicsDevice) : ArtTextures =
         let cc0 =
-            if useCc0Pack () then
-                Some(loadTexture device cc0TileAtlasRelativePath cc0TileAtlasWidth Sim.tilePixels)
-            else
-                None
-        let characterPath = if useCc0Pack () then cc0CharacterAtlasRelativePath else characterAtlasRelativePath
+            selectedGroundAtlasRelativePath ()
+            |> Option.map (fun path -> loadTexture device path cc0TileAtlasWidth cc0TileAtlasHeight)
         { TileAtlas = loadTexture device worldAtlasRelativePath worldAtlasWidth worldAtlasHeight
-          CharacterAtlas = loadTexture device characterPath characterAtlasWidth characterAtlasHeight
+          CharacterAtlas = loadTexture device (selectedCharacterAtlasRelativePath ()) cc0CharacterAtlasWidth cc0CharacterCellHeight
           InteriorAtlas = loadTexture device interiorAtlasRelativePath interiorAtlasWidth interiorAtlasHeight
           Cc0TileAtlas = cc0 }