feat(desktop): 增加可选昼光自动演示启动

[变更性质]
- 本提交新增可选的 Desktop 启动行为，不改变默认启动行为。

[新增功能]
- 设置 LV_AUTOPLAY_DAYLIGHT=1 时，初始世界和 StartNewGame 从黎明 tick 开始。
- 未设置该变量时继续从 tick 0 的夜晚状态开始。

[实现方案]
- 在 WorldBootstrap 中集中计算昼光起始 tick 和同步时间。
- 在 Game 中复用同一世界工厂，并增加黎明与默认状态回归测试。

[影响范围]
- 仅影响 Desktop 运行时代码和测试；Kernel 保持不变。
- 环境变量为显式 opt-in，不影响现有自动演示和普通启动路径。

3 files changed, 29 insertions, 3 deletions

diff --git a/src/LivingVillage.Desktop.Tests/DesktopTests.fs b/src/LivingVillage.Desktop.Tests/DesktopTests.fs
index 20cbbe9..667ab69 100644
--- a/src/LivingVillage.Desktop.Tests/DesktopTests.fs
+++ b/src/LivingVillage.Desktop.Tests/DesktopTests.fs
@@ -124,3 +124,18 @@ type DesktopTests () =
 
         Assert.IsTrue(day.WorldTint.R > day.WorldTint.G)
         Assert.IsTrue(day.WorldTint.G > day.WorldTint.B)
+
+    [<TestMethod>]
+    member _.DaylightAutoplayBootstrapStartsAtDawnAndPreservesDefaultStart () =
+        let dawnTick = 6L * Sim.ticksPerDay / 24L
+        let daylightWorld = WorldBootstrap.initialWorldForDaylight true 42UL Sim.npcCount
+        let defaultWorld = WorldBootstrap.initialWorldForDaylight false 42UL Sim.npcCount
+        let daylightProfile = M6Presentation.profileAtTick daylightWorld.Tick
+        let defaultProfile = M6Presentation.profileAtTick defaultWorld.Tick
+
+        Assert.AreEqual<int64>(dawnTick, daylightWorld.Tick)
+        Assert.IsTrue(abs (daylightWorld.Time - float dawnTick * Sim.dtSeconds) < 1e-9)
+        Assert.AreEqual<M6DayNight>(Day, daylightProfile.Mode)
+        Assert.AreEqual<int64>(0L, defaultWorld.Tick)
+        Assert.AreEqual<float>(0.0, defaultWorld.Time)
+        Assert.AreEqual<M6DayNight>(Night, defaultProfile.Mode)
diff --git a/src/LivingVillage.Desktop/Game.fs b/src/LivingVillage.Desktop/Game.fs
index 27e44a7..62102a7 100644
--- a/src/LivingVillage.Desktop/Game.fs
+++ b/src/LivingVillage.Desktop/Game.fs
@@ -97,6 +97,7 @@ type LivingVillageGame() as this =
     let autoplay = Environment.GetEnvironmentVariable("LV_AUTOPLAY") = "1"
     let autoplayFlow = Environment.GetEnvironmentVariable("LV_AUTOPLAY_FLOW") = "1"
     let sampleMode = Environment.GetEnvironmentVariable("LV_AUTOPLAY_SAMPLE") = "1"
+    let daylightAutoplay = Environment.GetEnvironmentVariable("LV_AUTOPLAY_DAYLIGHT") = "1"
     let automated = autoplay || autoplayFlow
     let modeName =
         if sampleMode then "sample"
@@ -124,7 +125,9 @@ type LivingVillageGame() as this =
     let mutable cjkAtlas = Unchecked.defaultof<Texture2D>
     let mutable pixel = Unchecked.defaultof<Texture2D>
     let renderPlan = VillageArt.sampleRenderPlan ()
-    let mutable world = WorldBootstrap.initialWorld 42UL Sim.npcCount
+    let createInitialWorld () =
+        WorldBootstrap.initialWorldForDaylight daylightAutoplay 42UL Sim.npcCount
+    let mutable world = createInitialWorld ()
     let mutable camera = Vector2.Zero
     let mutable avatarFacing = VillageArt.SouthFacing
     let mutable fpsFrames = 0
@@ -168,7 +171,7 @@ type LivingVillageGame() as this =
         this.CenterCamera()
 
     member private this.StartNewGame() =
-        world <- WorldBootstrap.initialWorld 42UL Sim.npcCount
+        world <- createInitialWorld ()
         this.ResetWorldView()
         menu <- menu |> MenuState.setCurrentWorld true |> MenuState.enterGame
         printfn $"new-game=ok seed=42 npcs={Sim.npcCount}"
diff --git a/src/LivingVillage.Desktop/WorldBootstrap.fs b/src/LivingVillage.Desktop/WorldBootstrap.fs
index 612931b..d6b906d 100644
--- a/src/LivingVillage.Desktop/WorldBootstrap.fs
+++ b/src/LivingVillage.Desktop/WorldBootstrap.fs
@@ -16,10 +16,13 @@ module WorldBootstrap =
 
     let private avatarSpawnPosition = tileCenter 31 25
 
-    let initialWorld (seed: uint64) (count: int) : World =
+    let private daylightStartTick = 6L * Sim.ticksPerDay / 24L
+
+    let initialWorldForDaylight (startAtDaylight: bool) (seed: uint64) (count: int) : World =
         if count < 0 || count > npcSpawnTiles.Length then
             invalidArg (nameof count) "Desktop bootstrap supports at most 30 NPCs."
 
+        let startTick = if startAtDaylight then daylightStartTick else 0L
         let baseWorld = Sim.initialWorldN seed count
         let avatar =
             { baseWorld.Avatar with
@@ -32,5 +35,10 @@ module WorldBootstrap =
                 { npc with Pos = tileCenter x y })
 
         { baseWorld with
+            Tick = startTick
+            Time = float startTick * Sim.dtSeconds
             Avatar = avatar
             Npcs = npcs }
+
+    let initialWorld (seed: uint64) (count: int) : World =
+        initialWorldForDaylight false seed count