feat(desktop): add Chinese village presentation prototype

[Change Nature]
- This commit adds a deterministic presentation-model feature, not MonoGame rendering.

[New Capability]
- Provide an immutable Jiangnan village scene with homes, waterways, paths, bridge, bamboo, and garden elements.
- Provide typed home transitions, four-way input mapping, tick animation, NPC styles, and Chinese stage-one labels.

[Implementation]
- Add the pure VillagePresentation module and six focused MSTest cases.
- Keep the model free of mutable global state and update only the required F# compile order.

[Impact]
- This commit affects the Desktop presentation and test projects only.
- Kernel behavior, Game.fs wiring, MonoGame drawing, and existing acceptance artifacts remain unchanged.

1 files changed, 171 insertions, 0 deletions

diff --git a/src/LivingVillage.Desktop/VillagePresentation.fs b/src/LivingVillage.Desktop/VillagePresentation.fs
new file mode 100644
index 0000000..95dc178
--- /dev/null
+++ b/src/LivingVillage.Desktop/VillagePresentation.fs
@@ -0,0 +1,171 @@
+namespace LivingVillage.Desktop
+
+module VillagePresentation =
+
+    (**
+       中文江南水乡阶段一样板的纯展示快照。
+
+       TilePosition 使用整数瓦片坐标；一个坐标单位代表一块场景瓦片，原点和
+       屏幕像素换算留给后续 MonoGame 组合层。SimulationTick 使用 int64，表示
+       Kernel 同一时间轴上的一个模拟 tick。PrototypeScene 以及其中的 record
+       和 list 都是不可变快照，调用方只能读取，不能把它们当作可变模拟状态；
+       本模块不保存可变全局状态，也不依赖 MonoGame。
+    **)
+
+    [<Struct>]
+    type TilePosition =
+        { X: int
+          Y: int }
+
+    [<Struct>]
+    type SimulationTick =
+        | SimulationTick of int64
+
+    [<Struct>]
+    type HomeId =
+        | HomeId of int
+
+    type VillageProp =
+        | WhiteWallDarkTileHome
+        | HomeDoor
+        | RiverChannel
+        | RiverBank
+        | StoneBridge
+        | StonePaving
+        | Bamboo
+        | VegetableGarden
+
+    type VillageElement =
+        { Prop: VillageProp
+          Position: TilePosition }
+
+    type Home =
+        { Id: HomeId
+          Door: TilePosition }
+
+    type PrototypeScene =
+        { Elements: VillageElement list
+          Homes: Home list
+          InitialPlayerPosition: TilePosition }
+
+    type Direction =
+        | North
+        | South
+        | West
+        | East
+
+    type DirectionInput =
+        | UpInput
+        | DownInput
+        | LeftInput
+        | RightInput
+        | NoInput
+
+    type CharacterAnimationFrame =
+        | FrameA
+        | FrameB
+
+    type CharacterStyle =
+        | StrawHatFarmer
+        | BlueApronVillager
+        | GreenScarfVillager
+
+    type HomeMode =
+        | Outside
+        | Inside of HomeId
+
+    type HomeTransitionError =
+        | NotNearHomeDoor
+        | AlreadyInsideHome of HomeId
+        | NotInsideHome
+        | HomeNotFound of HomeId
+
+    type StageOneCopy =
+        { Interact: string
+          Needs: string
+          Trade: string
+          EnterHome: string }
+
+    let private tile x y : TilePosition =
+        { X = x; Y = y }
+
+    let private element prop position : VillageElement =
+        { Prop = prop
+          Position = position }
+
+    let createScene () : PrototypeScene =
+        let home =
+            { Id = HomeId 1
+              Door = tile 6 5 }
+
+        { Elements =
+            [ element WhiteWallDarkTileHome (tile 6 4)
+              element HomeDoor home.Door
+              element StonePaving (tile 4 5)
+              element StonePaving (tile 5 5)
+              element StonePaving (tile 6 5)
+              element StonePaving (tile 7 5)
+              element RiverBank (tile 10 2)
+              element RiverBank (tile 10 3)
+              element RiverChannel (tile 10 4)
+              element RiverChannel (tile 10 5)
+              element StoneBridge (tile 10 4)
+              element Bamboo (tile 3 2)
+              element Bamboo (tile 3 3)
+              element VegetableGarden (tile 8 7)
+              element VegetableGarden (tile 9 7) ]
+          Homes = [ home ]
+          InitialPlayerPosition = tile 5 5 }
+
+    let scene : PrototypeScene =
+        createScene ()
+
+    let private manhattanDistance first second : int =
+        abs (first.X - second.X) + abs (first.Y - second.Y)
+
+    let isNearHomeDoor (position: TilePosition) (home: Home) : bool =
+        manhattanDistance position home.Door <= 1
+
+    let enterHome (position: TilePosition) (mode: HomeMode) : Result<HomeMode, HomeTransitionError> =
+        match mode with
+        | Inside homeId -> Error(AlreadyInsideHome homeId)
+        | Outside ->
+            match scene.Homes |> List.tryFind (isNearHomeDoor position) with
+            | Some home -> Ok(Inside home.Id)
+            | None -> Error NotNearHomeDoor
+
+    let exitHome (mode: HomeMode) : Result<HomeMode, HomeTransitionError> =
+        match mode with
+        | Outside -> Error NotInsideHome
+        | Inside homeId ->
+            if scene.Homes |> List.exists (fun home -> home.Id = homeId) then
+                Ok Outside
+            else
+                Error(HomeNotFound homeId)
+
+    let directionForInput (input: DirectionInput) : Direction option =
+        match input with
+        | UpInput -> Some North
+        | DownInput -> Some South
+        | LeftInput -> Some West
+        | RightInput -> Some East
+        | NoInput -> None
+
+    let private positiveModulo divisor value =
+        let remainder = value % divisor
+        if remainder < 0L then remainder + divisor else remainder
+
+    let animationFrame (SimulationTick tick) : CharacterAnimationFrame =
+        if positiveModulo 8L tick < 4L then FrameA else FrameB
+
+    let characterStyle (LivingVillage.Kernel.Sim.NpcId npcId) : CharacterStyle =
+        match ((npcId % 3) + 3) % 3 with
+        | 0 -> StrawHatFarmer
+        | 1 -> BlueApronVillager
+        | _ -> GreenScarfVillager
+
+    let stageOneCopy : StageOneCopy =
+        { Interact = "互动"
+          Needs = "需求"
+          Trade = "交易"
+          EnterHome = "进入民居" }