fix(incident): Alertmanager 告警補寫 frequency_stats → 歷史統計不再空白

根因：create_incident_for_approval 建立 Incident 時從未查詢 AnomalyCounter
     → frequency_snapshot 永遠 null → 歷史按鈕顯示「無建立時快照」
     signoz/sentry webhook 有寫，Alertmanager 路徑漏掉

修復：建立前 record_anomaly → 頻率快照存入 frequency_stats → PG 持久化
     失敗無害（try/except，不阻斷主流程）

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

apps/api/src/services/incident_service.py

@@ -32,6 +32,7 @@ from src.db.base import get_db_context
 from src.db.models import IncidentRecord
 from src.models.incident import (
     Incident,
+    IncidentFrequencyStats,
     IncidentStatus,
     Severity,
     Signal,
@@ -341,6 +342,40 @@ async def create_incident_for_approval(
 
     _affected_services = extract_affected_services(_labels, target_resource)
 
+    # 2026-04-27 ogt + Claude Sonnet 4.6: 補 frequency_stats 寫入
+    # 根因：Alertmanager 告警建立 Incident 時從未查詢 AnomalyCounter
+    #       → frequency_snapshot 永遠 null → 歷史統計顯示「無建立時快照」
+    # 修復：建立前先 record_anomaly，將頻率快照存入 frequency_stats
+    _freq_stats = None
+    try:
+        from src.services.anomaly_counter import get_anomaly_counter
+        _anomaly_sig = {
+            "alert_name": alertname or alert_type,
+            "service": (alert_labels or {}).get("service", target_resource),
+            "namespace": namespace,
+            "error_type": (alert_labels or {}).get("error_type", alert_type),
+        }
+        _freq = await get_anomaly_counter().record_anomaly(_anomaly_sig)
+        if _freq:
+            _freq_stats = _freq.to_dict()
+    except Exception as _freq_err:
+        logger.warning("incident_frequency_stats_failed", error=str(_freq_err))
+
+    _freq_model = None
+    if _freq_stats:
+        try:
+            _freq_model = IncidentFrequencyStats(
+                anomaly_key=_freq_stats.get("anomaly_key", "unknown"),
+                count_1h=_freq_stats.get("count_1h", 0),
+                count_24h=_freq_stats.get("count_24h", 0),
+                count_7d=_freq_stats.get("count_7d", 0),
+                count_30d=_freq_stats.get("count_30d", 0),
+                escalation_level=_freq_stats.get("escalation_level"),
+                auto_repair_count=_freq_stats.get("auto_repair_count", 0),
+            )
+        except Exception:
+            pass
+
     incident = Incident(
         status=IncidentStatus.INVESTIGATING,
         severity=severity,
@@ -349,6 +384,7 @@ async def create_incident_for_approval(
         proposal_ids=[UUID(approval_id)],
         notification_type=notification_type,  # ADR-073 Phase 2-2
         alert_category=alert_category,         # ADR-073 Phase 2-2
+        frequency_stats=_freq_model,
     )
 
     await incident_service.save_to_working_memory(incident)
@@ -813,8 +849,6 @@ class IncidentService:
 
             # 2. 建立 Incident (含頻率統計)
             # ADR-037: 統帥指示「重啟只是治標，太常發生的異常必須徹底解決」
-            from src.models.incident import IncidentFrequencyStats
-
             freq_stats = None
             if frequency_stats:
                 freq_stats = IncidentFrequencyStats(