feat: Anthropic 账号被动用量采样，页面默认展示被动数据

从上游 /v1/messages 响应头被动采集 5h/7d utilization 并存储到
Account.Extra，页面加载时直接读取本地数据而非调用外部 Usage API。
用户可点击"查询"按钮主动拉取最新数据，主动查询结果自动回写被动缓存。

后端:
- UpdateSessionWindow 合并采集 5h + 7d headers 为单次 DB 写入
- 新增 GetPassiveUsage 从 Extra 构建 UsageInfo (复用 estimateSetupTokenUsage)
- GetUsage 主动查询后 syncActiveToPassive 回写被动缓存
- passive_usage_ 前缀注册为 scheduler-neutral

前端:
- Anthropic 账号 mount/refresh 默认 source=passive
- 新增"被动采样"标签和"查询"按钮 (带 loading 动画)

backend/internal/handler/admin/account_handler.go

@@ -1496,7 +1496,7 @@ func (h *OAuthHandler) SetupTokenCookieAuth(c *gin.Context) {
 }
 
 // GetUsage handles getting account usage information
-// GET /api/v1/admin/accounts/:id/usage
+// GET /api/v1/admin/accounts/:id/usage?source=passive|active
 func (h *AccountHandler) GetUsage(c *gin.Context) {
 	accountID, err := strconv.ParseInt(c.Param("id"), 10, 64)
 	if err != nil {
@@ -1504,7 +1504,14 @@ func (h *AccountHandler) GetUsage(c *gin.Context) {
 		return
 	}
 
-	usage, err := h.accountUsageService.GetUsage(c.Request.Context(), accountID)
+	source := c.DefaultQuery("source", "active")
+
+	var usage *service.UsageInfo
+	if source == "passive" {
+		usage, err = h.accountUsageService.GetPassiveUsage(c.Request.Context(), accountID)
+	} else {
+		usage, err = h.accountUsageService.GetUsage(c.Request.Context(), accountID)
+	}
 	if err != nil {
 		response.ErrorFrom(c, err)
 		return