feat(usage): add usage stats export/import actions

src/i18n/locales/en.json

@@ -534,6 +534,11 @@
     "by_hour": "By Hour",
     "by_day": "By Day",
     "refresh": "Refresh",
+    "export": "Export",
+    "import": "Import",
+    "export_success": "Usage export downloaded",
+    "import_success": "Import complete: added {{added}}, skipped {{skipped}}, total {{total}}, failed {{failed}}",
+    "import_invalid": "Invalid usage export file",
     "chart_line_label_1": "Line 1",
     "chart_line_label_2": "Line 2",
     "chart_line_label_3": "Line 3",

src/i18n/locales/zh-CN.json

@@ -534,6 +534,11 @@
     "by_hour": "按小时",
     "by_day": "按天",
     "refresh": "刷新",
+    "export": "导出数据",
+    "import": "导入数据",
+    "export_success": "使用统计已导出",
+    "import_success": "导入完成：新增 {{added}}，跳过 {{skipped}}，总请求 {{total}}，失败 {{failed}}",
+    "import_invalid": "导入文件格式不正确",
     "chart_line_label_1": "曲线 1",
     "chart_line_label_2": "曲线 2",
     "chart_line_label_3": "曲线 3",