feat: 精油知识卡片加品牌元素 + 导出PDF修复

- 知识卡片: QR码(右上角)+品牌名+背景图+Logo
- 导出PDF: volumeLabel传name参数修复，单价列适配单位
- 导入api模块修复品牌数据加载

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

frontend/src/views/OilReference.vue

@@ -181,9 +181,16 @@
 
     <!-- Oil Knowledge Card Modal -->
     <div v-if="activeCard && activeCardName" class="modal-overlay" @mousedown.self="closeOilModal">
-      <div class="oil-card-modal">
+      <div class="oil-card-modal" style="position:relative;overflow:hidden">
-        <div class="oil-card-header">
+        <!-- Brand background -->
-          <div class="oil-card-header-content">
+        <div v-if="brand.brand_bg" style="position:absolute;inset:0;width:100%;height:100%;background-size:cover;background-position:center;opacity:0.08;pointer-events:none;z-index:0" :style="{ backgroundImage: `url('${brand.brand_bg}')` }"></div>
+        <!-- QR code -->
+        <div v-if="brand.qr_code" style="position:absolute;top:16px;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:48px;height:48px;object-fit:cover;border-radius:6px;box-shadow:0 2px 6px rgba(0,0,0,0.1)" />
+          <div v-if="brand.brand_name" style="font-size:7px;color:rgba(255,255,255,0.8);line-height:1.3;max-width:60px;white-space:pre-line;text-align:center">{{ brand.brand_name }}</div>
+        </div>
+        <div class="oil-card-header" style="position:relative;z-index:1">
+          <div class="oil-card-header-content" :style="brand.qr_code ? 'padding-right:70px' : ''">
             <span class="oil-card-emoji">{{ activeCard.emoji }}</span>
             <div>
               <h2 class="oil-card-title">{{ activeCardName }}</h2>
@@ -196,7 +203,7 @@
               </div>
             </div>
           </div>
-          <button class="btn-close btn-close-light" @click="closeOilModal">✕</button>
+          <button class="btn-close btn-close-light" @click="closeOilModal" style="z-index:4">✕</button>
         </div>
         <!-- Method badges -->
         <div class="oil-card-methods">
@@ -227,6 +234,10 @@
             <h4 class="oil-card-caution-title">⚠️ 注意事项</h4>
             <p>{{ activeCard.caution }}</p>
           </div>
+          <!-- Logo -->
+          <div v-if="brand.brand_logo" style="padding-top:8px">
+            <img :src="brand.brand_logo" crossorigin="anonymous" style="height:24px;opacity:0.7" />
+          </div>
           <div style="text-align:center;padding-top:12px">
             <button class="btn btn-outline btn-sm" @click="saveCardImage(activeCardName)">💾 保存图片</button>
           </div>
@@ -408,12 +419,19 @@ import { useRecipesStore } from '../stores/recipes'
 import { oilEn } from '../composables/useOilTranslation'
 import { getOilCard, setOilCard } from '../composables/useOilCards'
 import { showConfirm } from '../composables/useDialog'
+import { api } from '../composables/useApi'
 
 const auth = useAuthStore()
 const oils = useOilsStore()
 const recipeStore = useRecipesStore()
 const ui = useUiStore()
 
+// Brand data for card
+const brand = ref({})
+async function loadBrand() {
+  try { brand.value = await api.get('/api/brand') } catch {}
+}
+
 // Modal states
 const showDilution = ref(false)
 const showContra = ref(false)
@@ -637,6 +655,7 @@ async function openOilDetail(name) {
     activeCardName.value = name
     activeCard.value = card
     selectedOilName.value = null
+    loadBrand()
     // Pre-generate card image for instant save
     oilCardImageUrl.value = null
     await nextTick()
@@ -825,8 +844,9 @@ function exportPDF() {
     const en = getEnglishName(name)
     const bp = meta.bottlePrice != null ? '¥' + meta.bottlePrice.toFixed(0) : '--'
     const rp = meta.retailPrice != null ? '¥' + meta.retailPrice.toFixed(0) : '--'
-    const vol = volumeLabel(meta.dropCount)
+    const vol = volumeLabel(meta.dropCount, name)
-    const ppd = oils.pricePerDrop(name) ? '¥' + oils.pricePerDrop(name).toFixed(2) : '--'
+    const unit = oilPriceUnit(name)
+    const ppd = oils.pricePerDrop(name) ? '¥' + oils.pricePerDrop(name).toFixed(2) + '/' + unit : '--'
     rows += `<tr>
       <td>${name}</td>
       <td>${en}</td>
@@ -858,7 +878,7 @@ function exportPDF() {
 <h1>doTERRA 精油价目表 ${dateStr}</h1>
 <table>
   <thead>
-    <tr><th>精油</th><th>英文名</th><th>会员价</th><th>零售价</th><th>容量</th><th>单价/滴</th></tr>
+    <tr><th>精油</th><th>英文名</th><th>会员价</th><th>零售价</th><th>容量</th><th>单价</th></tr>
   </thead>
   <tbody>${rows}</tbody>
 </table>