fix: 配方卡片品牌样式与 initial commit 保持一致

- 背景图改用 div+background-image，opacity 从 0.06 恢复为 0.12
- 二维码位置改回 top:36px/right:24px，尺寸 54×54，加圆角和阴影
- 二维码下方新增品牌名称小字（7px）
- Logo 位置改回 bottom:60px，尺寸 height:60px，opacity 0.2

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/RecipeDetailOverlay.vue

@@ -39,18 +39,19 @@
         <!-- Card image (rendered by html2canvas) -->
         <div v-show="!cardImageUrl" ref="cardRef" class="export-card">
           <!-- Brand overlay layers -->
-          <img
+          <div
             v-if="brand.brand_bg"
-            :src="brand.brand_bg"
             class="card-brand-bg"
-            crossorigin="anonymous"
-          />
-          <img
-            v-if="brand.qr_code"
-            :src="brand.qr_code"
-            class="card-qr"
-            crossorigin="anonymous"
+            :style="{ backgroundImage: `url('${brand.brand_bg}')` }"
           />
+          <div v-if="brand.qr_code" class="card-qr-wrapper">
+            <img
+              :src="brand.qr_code"
+              class="card-qr"
+              crossorigin="anonymous"
+            />
+            <div v-if="brand.brand_name" class="card-qr-name">{{ brand.brand_name }}</div>
+          </div>
           <img
             v-if="brand.brand_logo"
             :src="brand.brand_logo"
@@ -997,32 +998,52 @@ async function saveRecipe() {
   inset: 0;
   width: 100%;
   height: 100%;
-  object-fit: cover;
-  opacity: 0.06;
+  background-size: cover;
+  background-position: center;
+  background-repeat: no-repeat;
+  opacity: 0.12;
   z-index: 0;
   pointer-events: none;
 }
 
-.card-qr {
+.card-qr-wrapper {
   position: absolute;
-  top: 16px;
-  right: 16px;
-  width: 64px;
-  height: 64px;
-  object-fit: contain;
-  z-index: 3;
-  opacity: 0.85;
+  top: 36px;
+  right: 24px;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 3px;
+  z-index: 2;
+}
+
+.card-qr {
+  width: 54px;
+  height: 54px;
+  object-fit: cover;
+  border-radius: 6px;
+  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.1);
+}
+
+.card-qr-name {
+  font-size: 7px;
+  color: var(--text-light, #8a7a6a);
+  text-align: center;
+  line-height: 1.3;
+  max-width: 68px;
+  white-space: pre-line;
 }
 
 .card-logo {
   position: absolute;
-  bottom: 16px;
+  bottom: 60px;
   left: 50%;
   transform: translateX(-50%);
-  height: 28px;
+  height: 60px;
   object-fit: contain;
-  z-index: 3;
-  opacity: 0.3;
+  z-index: 1;
+  opacity: 0.2;
+  pointer-events: none;
 }
 
 .card-brand-text {