refactor: 移除 infrastructure 目录 (#108)

* refactor: 迁移初始化 db 和 redis 到 repository

* refactor: 迁移 errors 到 pkg

backend/internal/pkg/errors/http.go

@@ -0,0 +1,21 @@
+package errors
+
+import "net/http"
+
+// ToHTTP converts an error into an HTTP status code and a JSON-serializable body.
+//
+// The returned body matches the project's Status shape:
+// { code, reason, message, metadata }.
+func ToHTTP(err error) (statusCode int, body Status) {
+	if err == nil {
+		return http.StatusOK, Status{Code: int32(http.StatusOK)}
+	}
+
+	appErr := FromError(err)
+	if appErr == nil {
+		return http.StatusOK, Status{Code: int32(http.StatusOK)}
+	}
+
+	cloned := Clone(appErr)
+	return int(cloned.Code), cloned.Status
+}