feat(phase-5-3): 모니터링 강화

logger.ts, metrics.ts, /api/metrics 추가
Version: e3bcb4ae

src/utils/circuit-breaker.ts

@@ -106,12 +106,24 @@ export class CircuitBreaker {
    * Get circuit statistics
    */
   getStats() {
+    const lastFailure = this.failures.length > 0
+      ? this.failures[this.failures.length - 1]
+      : null;
+
     return {
       state: this.state,
-      successCount: this.successCount,
-      failureCount: this.failureCount,
-      recentFailures: this.failures.length,
-      openedAt: this.openedAt,
+      failures: this.failures.length,
+      lastFailureTime: lastFailure ? new Date(lastFailure.timestamp) : undefined,
+      stats: {
+        totalRequests: this.successCount + this.failureCount,
+        totalFailures: this.failureCount,
+        totalSuccesses: this.successCount,
+      },
+      config: {
+        failureThreshold: this.failureThreshold,
+        resetTimeoutMs: this.resetTimeoutMs,
+        monitoringWindowMs: this.monitoringWindowMs,
+      },
     };
   }