站点背景功能优化、页脚上边距调整

frontend/lib/bg.ts

@@ -6,25 +6,18 @@ import type { CSSProperties } from "react";
 
 export type BgSurface = "site" | "admin";
 
-export type BgMode =
-  | "cover"
-  | "contain"
-  | "repeat"
-  | "repeat-x"
-  | "repeat-y"
-  | "stretch"
-  | "center";
+export type BgMode = "cover" | "contain" | "repeat" | "stretch";
 
 export const DEFAULT_BG_MODE: BgMode = "cover";
 
+/** 预览框按常见 PC 显示器 16:9（1920×1080）等比例缩放 */
+export const BG_PREVIEW_ASPECT = "16 / 9";
+
 export const BG_MODE_OPTIONS: { key: BgMode; label: string; hint: string }[] = [
-  { key: "cover", label: "覆盖铺满", hint: "裁切以铺满视口" },
-  { key: "contain", label: "完整显示", hint: "完整放入，两侧留底色" },
-  { key: "stretch", label: "拉伸填满", hint: "变形拉伸至视口" },
-  { key: "repeat", label: "平铺", hint: "按原尺寸重复铺满" },
-  { key: "repeat-x", label: "横向平铺", hint: "只沿水平方向重复" },
-  { key: "repeat-y", label: "纵向平铺", hint: "只沿垂直方向重复" },
-  { key: "center", label: "居中原图", hint: "不缩放，居中显示" },
+  { key: "cover", label: "填充", hint: "裁切铺满，适合照片" },
+  { key: "contain", label: "适应", hint: "整图可见，可能留边" },
+  { key: "repeat", label: "平铺", hint: "原尺寸重复，适合纹理" },
+  { key: "stretch", label: "拉伸", hint: "拉满屏幕，可能变形" },
 ];
 
 export interface SiteBgConfig {
@@ -72,14 +65,8 @@ function modeCSS(mode: BgMode): { size: string; repeat: string; position: string
       return { size: "contain", repeat: "no-repeat", position: "center" };
     case "repeat":
       return { size: "auto", repeat: "repeat", position: "0 0" };
-    case "repeat-x":
-      return { size: "auto", repeat: "repeat-x", position: "center top" };
-    case "repeat-y":
-      return { size: "auto", repeat: "repeat-y", position: "center top" };
     case "stretch":
       return { size: "100% 100%", repeat: "no-repeat", position: "center" };
-    case "center":
-      return { size: "auto", repeat: "no-repeat", position: "center" };
     default:
       return { size: "cover", repeat: "no-repeat", position: "center" };
   }