feat: 非精油产品(drop_count=1)显示"份"而非"滴"

oils store新增 unitLabel/unitLabelPlural，根据 dropCount 判断：
- 精油(dropCount>1): 滴/drop
- 护肤品等(dropCount=1): 份/portion
影响: 配方卡片、个人配方、库存匹配、去重提示

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

frontend/src/components/RecipeDetailOverlay.vue

@@ -64,7 +64,7 @@
             <ul style="list-style:none;margin-bottom:20px;padding:0">
               <li v-for="(ing, i) in cardIngredients" :key="i" class="ec-ing">
                 <span class="ec-oil-name">{{ getCardOilName(ing.oil) }}</span>
-                <span class="ec-drops">{{ ing.drops }} {{ cardLang === 'en' ? (ing.drops === 1 ? 'drop' : 'drops') : '滴' }}</span>
+                <span class="ec-drops">{{ ing.drops }} {{ oilsStore.unitLabelPlural(ing.oil, ing.drops, cardLang) }}</span>
                 <span class="ec-cost">{{ oilsStore.fmtPrice(oilsStore.pricePerDrop(ing.oil) * ing.drops) }}</span>
                 <span v-if="hasRetailForOil(ing.oil) && retailPerDrop(ing.oil) > oilsStore.pricePerDrop(ing.oil)" class="ec-retail">{{ oilsStore.fmtPrice(retailPerDrop(ing.oil) * ing.drops) }}</span>
               </li>