feat: Phase 6.6 知识库 RAG 增强 — 文档索引 + 语义检索 + KnowledgeProvider

- rag.Embedder: LLM API 文本向量化 (OpenAI-compatible)
- rag.KnowledgeStore: 文档分块 + 重叠窗口 + 余弦相似度搜索
- rag.Retriever: 高级知识检索 + 格式化摘要
- KnowledgeProvider: 子会话提供者，整合入编排管线
- knowledge_search / knowledge_ingest 工具
- EnrichmentData 管线全线支持 KnowledgeInfo

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/ai-core/internal/orchestrator/enrichment.go

@@ -7,6 +7,7 @@ type EnrichmentData struct {
 	MemorySummary  string
 	ThoughtOutline string
 	IoTSummary     string
+	KnowledgeInfo  string
 }
 
 // SessionEnrichmentStore is a thread-safe per-session cache for async

backend/ai-core/internal/orchestrator/orchestrator.go

@@ -243,10 +243,11 @@ func (o *Orchestrator) ProcessInput(
 		if o.enrichmentStore != nil {
 			prevEnrichment = o.enrichmentStore.Get(params.SessionID)
 			if prevEnrichment != nil {
-				logger.Printf("[orchestrator] 加载上一轮富化结果: memory=%t thought=%t iot=%t",
+				logger.Printf("[orchestrator] 加载上一轮富化结果: memory=%t thought=%t iot=%t knowledge=%t",
 					prevEnrichment.MemorySummary != "",
 					prevEnrichment.ThoughtOutline != "",
-					prevEnrichment.IoTSummary != "")
+					prevEnrichment.IoTSummary != "",
+					prevEnrichment.KnowledgeInfo != "")
 			}
 		}
 
@@ -273,6 +274,7 @@ func (o *Orchestrator) ProcessInput(
 			synthParams.MemorySummary = prevEnrichment.MemorySummary
 			synthParams.ThoughtOutline = prevEnrichment.ThoughtOutline
 			synthParams.IoTSummary = prevEnrichment.IoTSummary
+			synthParams.KnowledgeInfo = prevEnrichment.KnowledgeInfo
 		}
 
 		// 异步收集子会话结果，存入 enrichmentStore 供下一轮使用
@@ -300,6 +302,8 @@ func (o *Orchestrator) ProcessInput(
 					logger.Printf("[orchestrator] 通用对话子会话完成: %s", result.Summary)
 				case model.SubSessionIoT:
 					enriched.IoTSummary = result.Summary
+				case model.SubSessionKnowledge:
+					enriched.KnowledgeInfo = result.Summary
 					logger.Printf("[orchestrator] IoT 子会话完成: %s", result.Summary)
 				}
 			}

backend/ai-core/internal/orchestrator/synthesizer.go

@@ -36,6 +36,7 @@ type SynthesizeParams struct {
 	ThoughtOutline string             // 通用对话思考
 	IoTSummary     string             // IoT 操作摘要
 	DeviceContext  string             // 设备状态上下文
+	KnowledgeInfo  string             // 知识库检索摘要
 	Mode           string             // text / voice_assistant
 }
 
@@ -95,6 +96,14 @@ func (s *Synthesizer) buildSynthesizeMessages(params SynthesizeParams) []model.L
 		})
 	}
 
+	// 注入知识库检索结果
+	if params.KnowledgeInfo != "" && !strings.Contains(params.KnowledgeInfo, "未找到") {
+		messages = append(messages, model.LLMMessage{
+			Role:    model.RoleSystem,
+			Content: fmt.Sprintf("【知识库参考资料】\n%s", params.KnowledgeInfo),
+		})
+	}
+
 	// 注入对话历史
 	if len(params.DialogHistory) > 0 {
 		messages = append(messages, params.DialogHistory...)