refactor(management): rename GetUsage to GetUsageQueue and update routes/tests

- Renamed handler and test methods for better clarity on functionality.
- Updated route from `/v0/management/usage` to `/v0/management/usage-queue`.
- Adjusted integration and unit tests to reflect new naming and routes.

internal/api/handlers/management/usage.go

@@ -20,8 +20,8 @@ func (r usageQueueRecord) MarshalJSON() ([]byte, error) {
 	return json.Marshal(string(r))
 }
 
-// GetUsage pops queued usage records from the Redis-compatible usage queue.
-func (h *Handler) GetUsage(c *gin.Context) {
+// GetUsageQueue pops queued usage records from the usage queue.
+func (h *Handler) GetUsageQueue(c *gin.Context) {
 	if h == nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "handler unavailable"})
 		return