fix(patch): 适配 CLIProxyAPI v6.10.0 移除 Handler.usageStats 字段

usage.go 改为直接调用 usage.GetRequestStatistics() 全局单例，
不再依赖 Handler 结构体的 usageStats 字段。

.gitignore

@@ -0,0 +1 @@
+__pycache__/

patches/cliproxy/internal/api/handlers/management/usage.go

@@ -28,8 +28,9 @@ const defaultUsageDetailsLimit = 500
 func (h *Handler) GetUsageStatistics(c *gin.Context) {
 	var snapshot usage.StatisticsSnapshot
 	detailsLimit := parseUsageDetailsLimit(c, defaultUsageDetailsLimit)
-	if h != nil && h.usageStats != nil {
-		snapshot = h.usageStats.SnapshotWithOptions(usage.SnapshotOptions{
+	stats := usage.GetRequestStatistics()
+	if stats != nil {
+		snapshot = stats.SnapshotWithOptions(usage.SnapshotOptions{
 			IncludeDetails: detailsLimit != 0,
 			DetailLimit:    detailsLimit,
 		})
@@ -75,8 +76,9 @@ func parseUsageDetailsLimit(c *gin.Context, defaultLimit int) int {
 // ExportUsageStatistics returns a complete usage snapshot for backup/migration.
 func (h *Handler) ExportUsageStatistics(c *gin.Context) {
 	var snapshot usage.StatisticsSnapshot
-	if h != nil && h.usageStats != nil {
-		snapshot = h.usageStats.Snapshot()
+	stats := usage.GetRequestStatistics()
+	if stats != nil {
+		snapshot = stats.Snapshot()
 	}
 	c.JSON(http.StatusOK, usageExportPayload{
 		Version:    1,
@@ -87,7 +89,8 @@ func (h *Handler) ExportUsageStatistics(c *gin.Context) {
 
 // ImportUsageStatistics merges a previously exported usage snapshot into memory.
 func (h *Handler) ImportUsageStatistics(c *gin.Context) {
-	if h == nil || h.usageStats == nil {
+	stats := usage.GetRequestStatistics()
+	if stats == nil {
 		c.JSON(http.StatusBadRequest, gin.H{"error": "usage statistics unavailable"})
 		return
 	}
@@ -108,8 +111,8 @@ func (h *Handler) ImportUsageStatistics(c *gin.Context) {
 		return
 	}
 
-	result := h.usageStats.MergeSnapshot(payload.Usage)
-	snapshot := h.usageStats.Snapshot()
+	result := stats.MergeSnapshot(payload.Usage)
+	snapshot := stats.Snapshot()
 	c.JSON(http.StatusOK, gin.H{
 		"added":           result.Added,
 		"skipped":         result.Skipped,