feat: add DEFAULT_BACK_DESIGN and getEffectiveBackDesign

frontend/src/utils/cardLayout.js

@@ -58,6 +58,15 @@ export function getEffectiveDesign(project, cardKey) {
   return { ...base, ...overrides }
 }
 
+/**
+ * 合并项目级 back_design 与背面 card_overrides
+ */
+export function getEffectiveBackDesign(project) {
+  const base = JSON.parse(JSON.stringify(project?.back_design || DEFAULT_BACK_DESIGN))
+  const overrides = (project?.card_overrides || {})['back'] || {}
+  return { ...base, ...overrides }
+}
+
 /**
  * 计算数字牌 (1-10) 实际的花色位置（绝对像素）
  *  - 默认按 LAYOUT_POSITIONS
@@ -136,3 +145,14 @@ export const DEFAULT_DESIGN = {
   font_color: '#000000',
   corner_offset: { x: 0, y: 0 },
 }
+
+export const DEFAULT_BACK_DESIGN = {
+  background_color: '#1A237E',
+  border_color: '#C0A050',
+  border_width: 3,
+  pattern_color: null,
+  image: null,
+  image_dx: 0,
+  image_dy: 0,
+  image_scale: 1,
+}

frontend/src/utils/cardRenderer.js

@@ -12,6 +12,8 @@ import {
   isJoker,
   computeNumberPipPositions,
   getEffectiveDesign,
+  getEffectiveBackDesign,
+  DEFAULT_BACK_DESIGN,
 } from './cardLayout.js'
 
 const CARD_W = 750