rebuild: split core into separate repo; move wg-go integration to internal/ctr/corebind

- go.mod: require git.zkcoi.com/zkcoi/meshray/core, replace => ../Meshray
- internal/ctr/corebind: EnhancedBind + registry + adapter (wg-go integration isolated)
- cmd/mr-wg migrated from old core/cmd/meshray-core
- core/ removed; CHANGELOG updated; fix checkdb vet warning

cmd/checkdb/main.go

@@ -14,7 +14,7 @@ func main() {
 		log.Fatal(err)
 	}
 
-	fmt.Println("=== MeshRay 数据库表结构检查 ===\n")
+	fmt.Println("=== MeshRay 数据库表结构检查 ===")
 
 	// 检查所有表是否存在
 	tables := []string{