feat(management): add usage record retrieval endpoint

- Implemented `/v0/management/usage` endpoint for fetching queued usage records from Redis.
- Included validation for `count` parameter to ensure positive integers.
- Added unit tests for queue retrieval and validation, with authentication validation in integration tests.
- Updated management routing to include the new endpoint.

internal/api/handlers/management/usage.go

@@ -0,0 +1,55 @@
+package management
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+	"strconv"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/redisqueue"
+)
+
+type usageQueueRecord []byte
+
+func (r usageQueueRecord) MarshalJSON() ([]byte, error) {
+	if json.Valid(r) {
+		return append([]byte(nil), r...), nil
+	}
+	return json.Marshal(string(r))
+}
+
+// GetUsage pops queued usage records from the Redis-compatible usage queue.
+func (h *Handler) GetUsage(c *gin.Context) {
+	if h == nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "handler unavailable"})
+		return
+	}
+
+	count, errCount := parseUsageQueueCount(c.Query("count"))
+	if errCount != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": errCount.Error()})
+		return
+	}
+
+	items := redisqueue.PopOldest(count)
+	records := make([]usageQueueRecord, 0, len(items))
+	for _, item := range items {
+		records = append(records, usageQueueRecord(append([]byte(nil), item...)))
+	}
+
+	c.JSON(http.StatusOK, records)
+}
+
+func parseUsageQueueCount(value string) (int, error) {
+	value = strings.TrimSpace(value)
+	if value == "" {
+		return 1, nil
+	}
+	count, errCount := strconv.Atoi(value)
+	if errCount != nil || count <= 0 {
+		return 0, errors.New("count must be a positive integer")
+	}
+	return count, nil
+}