fix(merch/detail): 修复商户描述展开后滚动收起位置异常的问题

通过 key 强制重新渲染描述区域，重置滚动位置。合并重复的 toggleDesc 方法。

Sources:
- 61243b8 feat(merch/detail): add scroll hint for long product description

pages_promotion/merch/detail.vue

@@ -24,12 +24,12 @@
 						<text class="icox icox-xing"></text>
 					</view>
 					<view class="desc-wrap">
-						<view class="desc-text" :class="{ 'desc-expanded': isDescExpanded }" @click="toggleDesc">
-							<view>{{ merch.desc }}</view>
+						<view class="desc-text" :key="descKey" :class="{ 'desc-expanded': isDescExpanded }" @click="toggleDesc">
+							<view class="scroll-desc">{{ merch.desc }}</view>
 							<view class="scroll-hint" v-if="isShowScrollHint">
 								<text class="scroll-icon">↓</text>
 								<text class="scroll-text">上滑查看更多</text>
-							</view>							
+							</view>
 						</view>
 						<view class="expand-tip" v-if="merch.desc && merch.desc.length > 50" @click.stop="toggleDesc">
 							<text class="hint-arrow">{{ isDescExpanded ? '↑ 收起' : '↓ 展开' }}</text>
@@ -336,7 +336,8 @@ export default {
 			changeStyleDebounce: null,
 			headerHeightInited: false,
 			isDescExpanded: false,
-			isShowScrollHint: false
+			isShowScrollHint: false,
+			descKey: 0
 		};
 	},
 	mixins: [list],
@@ -360,22 +361,22 @@ export default {
 			});
 		},
 		toggleDesc() {
-			if (this.merch.desc) {
-				this.isDescExpanded = !this.isDescExpanded;
-			}
-		},
-		handleDescClick() {
 			if (!this.merch.desc) return;
-			this.isDescExpanded = !this.isDescExpanded;
-		},
-		toggleDesc() {
-			if (!this.merch.desc) return;
-			this.isDescExpanded = !this.isDescExpanded;
-			if (this.isDescExpanded && this.merch.desc.length > 200) {
-				this.isShowScrollHint = true;
-				setTimeout(() => {
-					this.isShowScrollHint = false;
-				}, 3000);
+
+			if (this.isDescExpanded) {
+				// 收起时切换 key 强制重新渲染，重置滚动位置
+				this.descKey = this.descKey === 0 ? 1 : 0;
+				this.isDescExpanded = false;
+				this.isShowScrollHint = false;
+			} else {
+				// 展开时直接设置展开状态
+				this.isDescExpanded = true;
+				if (this.merch.desc.length > 200) {
+					this.isShowScrollHint = true;
+					setTimeout(() => {
+						this.isShowScrollHint = false;
+					}, 3000);
+				}
 			}
 		},
 		initHeaderHeight() {