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/views/Inventory.vue

@@ -76,7 +76,7 @@
             class="match-ing"
             :class="{ missing: !ownedSet.has(ing.oil) }"
           >
-            {{ ing.oil }} {{ ing.drops }}滴
+            {{ ing.oil }} {{ ing.drops }}{{ oils.unitLabel(ing.oil) }}
           </span>
         </div>
         <div class="match-meta">