refactor(mcp-go): 拆除 search.Hybrid 残骸（T4.F）

- search.Hybrid 空转(NewHybrid 返空、Query 返 nil TODO)、构造后存进 Gateway
  却从不被调用（真实 RAG 走 rag.Engine）→ 纯误导性死重量
- 删 internal/search 包 + gateway.go 字段/构造参数 + main.go 接线
- build/vet 干净；wiki_search 不受影响（本就用 g.rag）

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

sundynix-mcp-go/cmd/server/main.go

@@ -15,7 +15,6 @@ import (
 	"github.com/sundynix/sundynix-mcp-go/internal/mcp"
 	"github.com/sundynix/sundynix-mcp-go/internal/memory"
 	"github.com/sundynix/sundynix-mcp-go/internal/rag"
-	"github.com/sundynix/sundynix-mcp-go/internal/search"
 
 	"github.com/sundynix/sundynix-shared/otelx"
 	"github.com/sundynix/sundynix-shared/prompts"
@@ -58,8 +57,7 @@ func main() {
 	defer b.Close()
 	log.Printf("[mcp_go] connected %s", natsURL)
 
-	engine := search.NewHybrid() // LLM Wiki 混合检索：Bleve + Milvus + Neo4j
-	mem := memory.Open(pgDSN)    // 偏好记忆：sundynix_user_profile（连不上则降级）
+	mem := memory.Open(pgDSN) // 偏好记忆：sundynix_user_profile（连不上则降级）
 	defer mem.Close()
 	hist := history.Open(redisAddr) // 会话短期历史：Redis（连不上则降级）
 	defer hist.Close()
@@ -104,7 +102,7 @@ func main() {
 		log.Printf("[mcp_go] subscribe prompts: %v", err)
 	}
 
-	gw := mcp.NewGateway(b, engine, mem, hist, ragEngine, pgDSN)
+	gw := mcp.NewGateway(b, mem, hist, ragEngine, pgDSN)
 
 	log.Println("[mcp_go] serving MCP over sundynix.tools.go.* (Ctrl-C to quit)")
 	if err := gw.Serve(ctx); err != nil && err != context.Canceled {