feat: 套装卡片显示折扣率（会员价后再X折）

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

frontend/src/composables/useKitCost.js

@@ -86,11 +86,23 @@ export function useKitCost() {
     return KITS.map(kit => {
       const perDrop = calcKitPerDrop(kit)
       const recipes = getKitRecipes(kit)
+      // Calculate discount rate for display
+      const resolved = kit.oils.map(name => resolveOilName(name))
+      const bc = kit.bottleCount || {}
+      let totalBP = 0
+      for (const name of resolved) {
+        const meta = oils.oilsMeta[name]
+        totalBP += meta ? meta.bottlePrice * (bc[name] || 1) : 0
+      }
+      const totalValue = totalBP + (kit.accessoryValue || 0)
+      const discountRate = totalValue > 0 ? Math.min(kit.price / totalValue, 1) : 1
+
       return {
         ...kit,
         perDrop,
         recipes,
         recipeCount: recipes.length,
+        discountRate,
       }
     }).sort((a, b) => a.recipeCount - b.recipeCount)
   })