refactor: 全面代码质量提升 — StringList→string[], strict 模式, 死代码清理

架构重构:
- StringList 类替换为不可变 string[]（消除 dataVersion hack，Zustand 自然检测变化）
- UndoRedoManager.undo/redo 返回新数组而非原地修改
- 删除 dataVersion 字段和 _bumpVersion()
- 启用 TypeScript strict 模式

死代码清理:
- 删除 string-list.ts, string-list.test.ts, use-path-validation.ts
- Rust AppError 保留供未来使用

功能修复:
- importFromJson 添加 try/catch
- handleClean 使用真实格式验证替代 () => true
- savePaths 保存前调用 backup_registry，处理部分保存失败
- importFromJson 校验非 object 类型输入

i18n 完善:
- MergePreview/StatusBar 硬编码中文 → t() 调用
- 新增 merge.* 和 status.* 翻译键

Rust 改进:
- registry.rs 抽取 load_paths/save_paths 通用函数，消除重复
- registry 新增 6 个单元测试（split/join/roundtrip）
- backup.rs 时间戳加毫秒防覆盖，回退路径改为 home_dir

元数据:
- package.json 名称→patheditor, 版本→4.0.0
- 新增 CHANGELOG.md
- 移除 UndoRedoButtons 废弃注释
- tsconfig 添加 strict:true

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

src/i18n/locales/en.json

@@ -27,6 +27,11 @@
     "lightMode": "Light Mode",
     "language": "Language"
   },
+  "merge": {
+    "system": "System",
+    "user": "User",
+    "source": "Source"
+  },
   "status": {
     "normal": "Ready",
     "readonly": "Read-only mode — Administrator privileges required for editing",
@@ -36,6 +41,11 @@
     "deleted": "Deleted {{count}} path(s)",
     "loaded": "Loaded {{sysCount}} system and {{userCount}} user paths",
     "dragFolderOnly": "Only folders can be dropped",
+    "loading": "Loading...",
+    "modified": "Modified",
+    "readonly_label": "Read-only",
+    "light": "Light",
+    "dark": "Dark",
     "adminWarning": "Running without administrator privileges, some features are disabled"
   },
   "dialog": {