fix: 品牌标语说明统一格式 + 对齐在卡片和预览生效

- 标签改为"✍ 品牌名称或标语"+"显示在二维码下方"（与其他说明格式一致）
- 靠左/居中/靠右在预览和配方卡片中都生效
- 修复align-items:center覆盖textAlign的问题

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/RecipeDetailOverlay.vue

@@ -52,7 +52,7 @@
           <!-- Background image overlay -->
           <div v-if="brand.brand_bg" style="position:absolute;inset:0;width:100%;height:100%;background-size:cover;background-position:center;opacity:0.12;pointer-events:none;z-index:0" :style="{ backgroundImage: `url('${brand.brand_bg}')` }"></div>
           <!-- QR: top-right -->
-          <div v-if="brand.qr_code" style="position:absolute;top:20px;right:16px;display:flex;flex-direction:column;align-items:center;gap:3px;z-index:3">
+          <div v-if="brand.qr_code" style="position:absolute;top:20px;right:16px;display:flex;flex-direction:column;gap:3px;z-index:3" :style="{ alignItems: (brand.brand_align === 'left' ? 'flex-start' : brand.brand_align === 'right' ? 'flex-end' : 'center') }">
             <img :src="brand.qr_code" crossorigin="anonymous" style="width:54px;height:54px;object-fit:cover;border-radius:6px;box-shadow:0 2px 6px rgba(0,0,0,0.1)" />
             <div v-if="brand.brand_name" :style="{ textAlign: brand.brand_align || 'center' }" style="font-size:7px;color:var(--text-light);line-height:1.3;max-width:68px;white-space:pre-line">{{ brand.brand_name }}</div>
           </div>