feat: 全部页面添加 MonthPicker 月份切换

新增 MonthPicker 的页面(6个):
- CostPage: 成本与库存管理
- SKUPage: 商品SKU管理
- PlatformPage: 平台与优惠管理
- MemberPage: 会员与复购管理
- SiteSelectionPage: 门店选址分析
- DataQualityPage: 数据质量看板

容器+子组件添加 MonthPicker(2个页面, 11个子组件):
- StoreExpensePage: 门店营业费用分析(10个子组件全部传month)
- CostAnalysisPage/StoreTab: 门店成本tab

跳过(后端不支持month参数):
- RiskPage: 风险管理(全量视图, 不按月过滤)
- TimePage: 时间段分析(全量视图, 不按月过滤)

client/src/pages/CostPage.tsx

@@ -9,6 +9,7 @@ import { Badge } from '@/components/Badge'
 import { formatCurrency, formatNumber, formatPercent } from '@/lib/utils'
 import { useState, useMemo } from 'react'
 import { BarChart, Bar, XAxis, YAxis, CartesianGrid, Tooltip, ResponsiveContainer, ScatterChart, Scatter } from 'recharts'
+import { MonthPicker } from '@/components/MonthPicker'
 
 const PAGE_SIZE = 15
 
@@ -16,20 +17,21 @@ export function CostPage() {
   const [costPage, setCostPage] = useState(1)
   const [invPage, setInvPage] = useState(1)
   const [catPage, setCatPage] = useState(1)
+  const [month, setMonth] = useState('2026-04')
 
   const { data: costData, isLoading: costLoading } = useQuery({
-    queryKey: ['cost/comparison'],
-    queryFn: () => api.get('/cost/comparison'),
+    queryKey: ['cost/comparison', month],
+    queryFn: () => api.get('/cost/comparison', { params: { month } }),
   })
 
   const { data: invData, isLoading: invLoading } = useQuery({
-    queryKey: ['cost/inventory'],
-    queryFn: () => api.get('/cost/inventory'),
+    queryKey: ['cost/inventory', month],
+    queryFn: () => api.get('/cost/inventory', { params: { month } }),
   })
 
   const { data: catData, isLoading: catLoading } = useQuery({
-    queryKey: ['cost/category-benchmark'],
-    queryFn: () => api.get('/cost/category-benchmark'),
+    queryKey: ['cost/category-benchmark', month],
+    queryFn: () => api.get('/cost/category-benchmark', { params: { month } }),
   })
 
   const costRows = (costData as any)?.data || []
@@ -67,9 +69,12 @@ export function CostPage() {
 
   return (
     <div className="space-y-4">
-      <div>
-        <h1 className="text-xl font-bold">成本与库存管理</h1>
-        <p className="mt-0.5 text-xs text-muted-foreground">理论vs实际成本 · 原料分类差异 · 库存效率 · 2026年4月</p>
+      <div className="flex items-center justify-between">
+        <div>
+          <h1 className="text-xl font-bold">成本与库存管理</h1>
+          <p className="mt-0.5 text-xs text-muted-foreground">理论vs实际成本 · 原料分类差异 · 库存效率 · {month}</p>
+        </div>
+        <MonthPicker month={month} onChange={setMonth} />
       </div>
 
       {/* 概览指标 */}