fix(desktop): 标题菜单光标与文字分列不再叠印

根因：页面标题行（panelY+24）与首行内容（MenuTopY）同为 y=320 造成两串文字叠印。修复：TitleScreen 布局新增 HeadingY/FirstItemY 分层与独立光标列（CursorX/CursorWidth/TextX），selectionRects 纯函数返回光标与文字矩形，回归测试断言逐行矩形不相交且标题行净空≥32px；渲染改为光标、文字分别绘制。

1 files changed, 31 insertions, 2 deletions

diff --git a/src/LivingVillage.Desktop/TitleScreen.fs b/src/LivingVillage.Desktop/TitleScreen.fs
index 8b1c5d5..00cf5b8 100644
--- a/src/LivingVillage.Desktop/TitleScreen.fs
+++ b/src/LivingVillage.Desktop/TitleScreen.fs
@@ -24,7 +24,31 @@ module TitleScreen =
           PanelX: int
           PanelY: int
           PanelWidth: int
-          PanelHeight: int }
+          PanelHeight: int
+          HeadingY: int
+          FirstItemY: int
+          CursorX: int
+          CursorWidth: int
+          TextX: int }
+
+    type TextRect =
+        { X: int
+          Y: int
+          Width: int
+          Height: int }
+
+    let rectsDisjoint (a: TextRect) (b: TextRect) : bool =
+        a.X + a.Width <= b.X
+        || b.X + b.Width <= a.X
+        || a.Y + a.Height <= b.Y
+        || b.Y + b.Height <= a.Y
+
+    /// Cursor and label rectangles for one menu row. The cursor is drawn in its own
+    /// column; the label always starts to the right of it, so they can never overprint.
+    let selectionRects (layout: TitleLayout) (rowIndex: int) : TextRect * TextRect =
+        let y = layout.FirstItemY + rowIndex * layout.MenuLineHeight
+        { X = layout.CursorX; Y = y; Width = layout.CursorWidth; Height = 16 },
+        { X = layout.TextX; Y = y; Width = layout.PanelX + layout.PanelWidth - layout.TextX - 24; Height = 16 }
 
     // Palette mirrors the VillageArt atlas: roof (45,49,57)/(30,33,38), water (54,116,145),
     // lantern paper (212,92,74). Purely decorative reuse of existing art colors.
@@ -82,4 +106,9 @@ module TitleScreen =
           PanelX = (width - panelWidth) / 2
           PanelY = height / 2 - 64
           PanelWidth = panelWidth
-          PanelHeight = min 360 (height - height / 2 - 40) }
+          PanelHeight = min 360 (height - height / 2 - 40)
+          HeadingY = height / 2 - 64 + 20
+          FirstItemY = height / 2 - 64 + 60
+          CursorX = (width - panelWidth) / 2 + 24
+          CursorWidth = 20
+          TextX = (width - panelWidth) / 2 + 24 + 20 + 12 }