fix(flywheel-stats): 修補 FlywheelStatsService 三個欄位錯誤

- KnowledgeEntryRecord.vectorized → embedding.is_(None) (欄位不存在)
- IncidentRecord.id → IncidentRecord.incident_id (主鍵名稱)
- 修復後 /api/v1/stats/flywheel nodes 不再全部回傳 unknown

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

apps/api/src/services/flywheel_stats_service.py

@@ -219,9 +219,9 @@ class FlywheelStatsService:
             today_start = now.replace(hour=0, minute=0, second=0, microsecond=0)
 
             async with get_db_context() as db:
-                # 未向量化數量
+                # 未向量化數量 (embedding IS NULL = 未向量化)
                 unvectorized_q = await db.execute(
-                    select(func.count()).where(KnowledgeEntryRecord.vectorized.is_(False))
+                    select(func.count()).where(KnowledgeEntryRecord.embedding.is_(None))
                 )
                 unvectorized = unvectorized_q.scalar_one_or_none() or 0
 
@@ -256,7 +256,7 @@ class FlywheelStatsService:
 
             async with get_db_context() as db:
                 # alertname NULL 率
-                total_q = await db.execute(select(func.count(IncidentRecord.id)))
+                total_q = await db.execute(select(func.count(IncidentRecord.incident_id)))
                 total = total_q.scalar_one_or_none() or 0
 
                 null_q = await db.execute(