fix: 修复 5 个 bug + 备份警告丢失

- BUG 1: undo/redo 后持久化 disabled 状态到 disabled.json
- BUG 2: expand_env_vars 增加缓冲区不足检测（result > required）
- BUG 3: E2E mock load_disabled_state 返回格式从对象改为数组
- BUG 4: 双 hive 保存失败时同时显示两个错误原因
- BUG 5: 导入 both 合并为单条 undo 记录（新增 IMPORT_BOTH 操作类型）
- 备份失败后保存成功时显示"保存成功（备份失败）"而非覆盖警告

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

src/i18n/locales/en.json

@@ -38,6 +38,7 @@
     "readonly": "Read-only mode — Administrator privileges required for editing",
     "saving": "Saving...",
     "saved": "Saved successfully",
+    "saved_without_backup": "Saved (backup failed)",
     "error": "Operation failed",
     "warning_backup": "Backup creation failed, save will proceed without backup",
     "deleted": "Deleted {{count}} path(s)",

src/i18n/locales/zh-CN.json

@@ -38,6 +38,7 @@
     "readonly": "只读模式 — 需要管理员权限才能编辑",
     "saving": "正在保存...",
     "saved": "保存成功",
+    "saved_without_backup": "保存成功（备份失败）",
     "error": "操作失败",
     "warning_backup": "备份创建失败，保存将继续但不生成备份",
     "deleted": "已删除 {{count}} 个路径",