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
+}

internal/api/handlers/management/usage_test.go

@@ -0,0 +1,98 @@
+package management
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/redisqueue"
+)
+
+func TestGetUsagePopsRequestedRecords(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	withManagementUsageQueue(t, func() {
+		redisqueue.Enqueue([]byte(`{"id":1}`))
+		redisqueue.Enqueue([]byte(`{"id":2}`))
+		redisqueue.Enqueue([]byte(`{"id":3}`))
+
+		rec := httptest.NewRecorder()
+		ginCtx, _ := gin.CreateTestContext(rec)
+		ginCtx.Request = httptest.NewRequest(http.MethodGet, "/v0/management/usage?count=2", nil)
+
+		h := &Handler{}
+		h.GetUsage(ginCtx)
+
+		if rec.Code != http.StatusOK {
+			t.Fatalf("status = %d, want %d body=%s", rec.Code, http.StatusOK, rec.Body.String())
+		}
+
+		var payload []json.RawMessage
+		if errUnmarshal := json.Unmarshal(rec.Body.Bytes(), &payload); errUnmarshal != nil {
+			t.Fatalf("unmarshal response: %v", errUnmarshal)
+		}
+		if len(payload) != 2 {
+			t.Fatalf("response records = %d, want 2", len(payload))
+		}
+		requireRecordID(t, payload[0], 1)
+		requireRecordID(t, payload[1], 2)
+
+		remaining := redisqueue.PopOldest(10)
+		if len(remaining) != 1 || string(remaining[0]) != `{"id":3}` {
+			t.Fatalf("remaining queue = %q, want third item only", remaining)
+		}
+	})
+}
+
+func TestGetUsageInvalidCountDoesNotPop(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	withManagementUsageQueue(t, func() {
+		redisqueue.Enqueue([]byte(`{"id":1}`))
+
+		rec := httptest.NewRecorder()
+		ginCtx, _ := gin.CreateTestContext(rec)
+		ginCtx.Request = httptest.NewRequest(http.MethodGet, "/v0/management/usage?count=0", nil)
+
+		h := &Handler{}
+		h.GetUsage(ginCtx)
+
+		if rec.Code != http.StatusBadRequest {
+			t.Fatalf("status = %d, want %d body=%s", rec.Code, http.StatusBadRequest, rec.Body.String())
+		}
+
+		remaining := redisqueue.PopOldest(10)
+		if len(remaining) != 1 || string(remaining[0]) != `{"id":1}` {
+			t.Fatalf("remaining queue = %q, want original item", remaining)
+		}
+	})
+}
+
+func withManagementUsageQueue(t *testing.T, fn func()) {
+	t.Helper()
+
+	prevQueueEnabled := redisqueue.Enabled()
+	redisqueue.SetEnabled(false)
+	redisqueue.SetEnabled(true)
+
+	defer func() {
+		redisqueue.SetEnabled(false)
+		redisqueue.SetEnabled(prevQueueEnabled)
+	}()
+
+	fn()
+}
+
+func requireRecordID(t *testing.T, raw json.RawMessage, want int) {
+	t.Helper()
+
+	var payload struct {
+		ID int `json:"id"`
+	}
+	if errUnmarshal := json.Unmarshal(raw, &payload); errUnmarshal != nil {
+		t.Fatalf("unmarshal record: %v", errUnmarshal)
+	}
+	if payload.ID != want {
+		t.Fatalf("record id = %d, want %d", payload.ID, want)
+	}
+}