feat: webUI 文本文件编辑/保存 + 相关改动

- FileViewer 新增文本编辑模式（textarea + 保存/取消 + Ctrl+S）
- 后端 /api/files POST 新增 type=write 原子写入
- i18n 补充编辑相关文案（en/zh-CN）
- searxng-search: 加强 web_search 自动搜索条件
- worktree/next.config: 路径比较与 allowedDevOrigins 优化

pi-web/lib/i18n/messages/en.ts

@@ -304,6 +304,16 @@ export const enLocale: LocalePlugin = {
     "i18n.mentionSelectedLines": "Mention selected lines",
     "i18n.disableWrap": "Disable word wrap",
     "i18n.enableWrap": "Enable word wrap",
+    "i18n.editFile": "Edit file",
+    "i18n.stopEditing": "Stop editing",
+    "i18n.saveFile": "Save file",
+    "i18n.saveShortcut": "Save (Ctrl/Cmd+S)",
+    "i18n.discardChanges": "Discard unsaved changes",
+    "i18n.saveError": "Could not save file: {error}",
+    "i18n.closeWithoutSaving": "You have unsaved changes. Discard them and exit editing?",
+    "i18n.editing": "Editing",
+    "i18n.unsaved": "unsaved changes",
+    "i18n.readOnly": "Read-only",
     "i18n.htmlPreview": "HTML preview",
     "i18n.previewFile": "Preview {file}",
     "i18n.invalidMermaid": "Invalid Mermaid diagram",