feat: 어댑터/인터페이스/클라이언트 유량제어 메트릭 API 추가

InflowTargetMetricController / InflowTargetMetricService / TargetMetricDTO 추가.
어댑터·인터페이스·클라이언트별 허용/초당거절/임계거절 카운터 조회 및 초기화 API 제공.
단위테스트: InflowTargetMetricServiceTest(26건), InflowTargetMetricControllerTest(16건).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main/java/com/eactive/eai/manage/inflow/TargetMetricDTO.java

@@ -0,0 +1,44 @@
+package com.eactive.eai.manage.inflow;
+
+/**
+ * 어댑터/인터페이스/클라이언트 메트릭 DTO.
+ */
+public class TargetMetricDTO {
+
+    private String  targetId;
+    private String  targetType;   // "ADAPTER" | "INTERFACE" | "CLIENT"
+    private boolean activate;
+    private long    allowed;
+    private long    rejectedPerSecond;
+    private long    rejectedThreshold;
+    private long    totalRequests;
+    private double  rejectRatio;
+    private long    lastResetTime;
+
+    public String getTargetId()                       { return targetId; }
+    public void   setTargetId(String targetId)        { this.targetId = targetId; }
+
+    public String getTargetType()                     { return targetType; }
+    public void   setTargetType(String targetType)    { this.targetType = targetType; }
+
+    public boolean isActivate()                       { return activate; }
+    public void    setActivate(boolean activate)      { this.activate = activate; }
+
+    public long getAllowed()                           { return allowed; }
+    public void setAllowed(long allowed)              { this.allowed = allowed; }
+
+    public long getRejectedPerSecond()                          { return rejectedPerSecond; }
+    public void setRejectedPerSecond(long rejectedPerSecond)    { this.rejectedPerSecond = rejectedPerSecond; }
+
+    public long getRejectedThreshold()                          { return rejectedThreshold; }
+    public void setRejectedThreshold(long rejectedThreshold)    { this.rejectedThreshold = rejectedThreshold; }
+
+    public long getTotalRequests()                    { return totalRequests; }
+    public void setTotalRequests(long totalRequests)  { this.totalRequests = totalRequests; }
+
+    public double getRejectRatio()                    { return rejectRatio; }
+    public void   setRejectRatio(double rejectRatio)  { this.rejectRatio = rejectRatio; }
+
+    public long getLastResetTime()                    { return lastResetTime; }
+    public void setLastResetTime(long lastResetTime)  { this.lastResetTime = lastResetTime; }
+}