fix(knowledge): I2+I3 首席架構師 Important 修復 — 依賴注入 + exception 細分

I2: KnowledgeService 移至 DecisionManager.__init__ 注入
    _query_kb_context_inner 使用 self._knowledge_svc，移除函數內 import 耦合

I3: _query_kb_context exception 細分
    - asyncio.TimeoutError → warning (預期降級)
    - ConnectionError/OSError → warning (Ollama 連線問題，預期降級)
    - Exception → error (非預期，提升監控可見性)

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

apps/api/src/services/decision_manager.py

@@ -374,6 +374,10 @@ class DecisionManager:
 
     def __init__(self):
         self._openclaw = get_openclaw()
+        # I2 修復 (首席架構師 Review): 注入 KnowledgeService 避免函數內 import 耦合
+        # 2026-04-04 Claude Code
+        from src.services.knowledge_service import get_knowledge_service
+        self._knowledge_svc = get_knowledge_service()
 
     async def get_or_create_decision(
         self,
@@ -550,14 +554,12 @@ class DecisionManager:
 
     async def _query_kb_context_inner(self, incident: Incident) -> str:
         """KB RAG 實際查詢邏輯，由 _query_kb_context 包裝 timeout 後呼叫"""
-        from src.services.knowledge_service import get_knowledge_service
         query_parts = list(incident.affected_services)
         if incident.signals:
             query_parts.insert(0, getattr(incident.signals[0], "alert_name", ""))
         query = " ".join(filter(None, query_parts))
 
-        svc = get_knowledge_service()
-        results = await svc.semantic_search(query, limit=3, threshold=0.4)
+        results = await self._knowledge_svc.semantic_search(query, limit=3, threshold=0.4)
         if not results:
             return ""
 
@@ -593,8 +595,13 @@ class DecisionManager:
         except asyncio.TimeoutError:
             logger.warning("kb_rag_timeout", incident_id=incident.incident_id)
             return ""
+        except (ConnectionError, OSError) as e:
+            # Ollama 連線問題，預期可降級
+            logger.warning("kb_rag_connection_error", incident_id=incident.incident_id, error=str(e))
+            return ""
         except Exception as e:
-            logger.warning("kb_rag_failed", incident_id=incident.incident_id, error=str(e))
+            # 非預期錯誤，用 error 級別方便監控
+            logger.error("kb_rag_unexpected_error", incident_id=incident.incident_id, error=str(e))
             return ""
 
     async def _dual_engine_analyze(