fix(alerter): Ollama 恢復告警去重修復 — per-host key + 1h TTL

根因：
1. dedup_key 固定為 "alert:recovery"，GCP-A 每 10min 健康閃爍就觸發重發
2. 三層容災下不同主機恢復共用同一個 key，互相污染

修法：
- dedup key 改為 "alert:recovery:{safe_host}"，各主機獨立 dedup
- RECOVERY_DEDUP_TTL_SEC = 3600（1h），GCP 持續閃爍只報一次

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

apps/api/src/services/failover_alerter.py

@@ -18,7 +18,8 @@ from typing import Any
 import structlog
 
 TAIPEI_TZ = timezone(timedelta(hours=8))
-DEDUP_TTL_SEC = 600  # 10 min
+DEDUP_TTL_SEC = 600  # 10 min（故障切換用）
+RECOVERY_DEDUP_TTL_SEC = 3600  # 1h — GCP 健康閃爍時 1 小時內不重複告警
 QUOTA_DEDUP_TTL_SEC = 86400  # 24h（每日 quota 告警只發一次）
 
 logger = structlog.get_logger(__name__)
@@ -69,11 +70,16 @@ class FailoverAlerter:
         logger.info("failover_alert_sent", to_provider=to_provider)
 
     async def alert_recovery(self, event: dict[str, Any]) -> None:
-        """Ollama 自動恢復告警 — 10min dedup
+        """Ollama 自動恢復告警 — 1h dedup per host
         # 2026-05-03 ogt: ADR-110 三層容災，恢復主機從 event["recovered_host"] 動態讀取
+        # 2026-05-04 ogt: dedup key 加 recovered_host + 改 1h TTL
+        #   原 key 固定 "alert:recovery" → GCP-A 每 10min 閃爍就重發
         """
-        dedup_key = "alert:recovery"
-        if not await self._check_dedup(dedup_key, ttl=DEDUP_TTL_SEC):
+        recovered_host = event.get("recovered_host", event.get("to_provider", "ollama"))
+        # sanitize host → 只留 IP/hostname 部分，拿掉 http:// 前綴與 port
+        safe_host = str(recovered_host).replace("http://", "").replace("/", "_").replace(":", "_")
+        dedup_key = f"alert:recovery:{safe_host}"
+        if not await self._check_dedup(dedup_key, ttl=RECOVERY_DEDUP_TTL_SEC):
             logger.debug("recovery_alert_dedup_skipped")
             return
 
@@ -82,8 +88,6 @@ class FailoverAlerter:
         from_provider = event.get("from_provider", event.get("from", "?"))
         to_provider = event.get("to_provider", event.get("to", "ollama"))
         recovery_time = event.get("recovery_time", datetime.now(TAIPEI_TZ).isoformat())
-        # 2026-05-03 ogt: ADR-110 — 恢復主機動態，不再硬編碼 111
-        recovered_host = event.get("recovered_host", to_provider)
 
         msg = (
             f"*Ollama 自動恢復*\n\n"