fix(host_aggregator): total=1 時 total//2=0 導致服務全 up 仍顯示 unhealthy

112(Kali) 和 120(K3s) 各只有 1 個服務，down_count=0 >= total//2=0
永遠成立 → 永遠 unhealthy。改為 total > 1 才套用 >=half 門檻。

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

apps/api/src/services/host_aggregator.py

@@ -391,9 +391,10 @@ class HostAggregator:
         degraded_count = sum(1 for s in services if s.status == "degraded")
         total = len(services)
 
+        # 2026-04-09 Claude Sonnet 4.6: 修正 total=1 時 total//2=0 導致永遠 unhealthy
         if down_count == total:
             host_status: Literal["healthy", "degraded", "unhealthy", "unreachable"] = "unreachable"
-        elif down_count >= total // 2:
+        elif total > 1 and down_count >= total // 2:
             host_status = "unhealthy"
         elif down_count > 0 or degraded_count > 0:
             host_status = "degraded"