feat(ui): revert indicator with undo/redo, message list, and attachment restore (#1279)

* feat(ui): revert indicator with undo/redo, message list, and attachment restore

Add bidirectional undo/redo with redo stack navigation and expandable
revert indicator in StatusRow. List reverted messages with inline
revert/fork actions. Restore file attachments on revert.

- Add revert indicator with count, expandable popover, per-button spinner
- Restore file/image attachments when reverting to a message
- Clear previous attachments on revert when target has none
- Restore-all bypasses redo stack for direct unrevert
- Survive popover close/reopen without losing loading state
- Fix flash when sending message after revert
- Fix count disappearing on browser refresh
- Remove dead code (undoStack, getRevertHistory, fork-from-here)
- Fix toast grammar (Undid -> Reverted, Redid -> Redone)
- Add i18n keys for revert popover across all locales

* fix(ui): Greptile review fixes and i18n for revert toasts

- Fix handleSlashUndo toast always showing [No text] (moved getSyncParts before revertToMessage)
- Add inputStore rollback in revertToMessage catch (restore attachments + text on API failure)
- Change portal ID to per-session (prevent multi-session collisions)
- Add i18n keys for undo/redo/restored toasts across all 7 locales
- Use formatMessage in store for localized toast strings

* fix(ui): add missing sessionId to click-outside effect deps

* fix(ui): remove unused sessionActions import in ChatMessage

* fix(ui): derive revert dock from session state

---------

Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/ui/src/lib/i18n/messages/zh-CN.ts

@@ -1368,6 +1368,19 @@ export const dict: Record<I18nKey, string> = {
   'chat.statusRow.tasksTitle': '任务',
   'chat.statusRow.summary.activeLeft': '{active} 个活跃 · 剩余 {left} 个',
   'chat.statusRow.aborted': '已中止',
+  'chat.revertIndicator.redo': '重做',
+  'chat.revertIndicator.redoAria': '重做 — 恢复已撤回的消息',
+  'chat.revertPopover.title': '已撤回',
+  'chat.revertPopover.noTextContent': '无文本内容',
+  'chat.revertPopover.forkFromHere': '从此处分支',
+  'chat.revertPopover.forkFromMessage': '从此消息分支',
+  'chat.revertPopover.restoreAll': '恢复全部',
+  'chat.revertPopover.restore': '恢复',
+  'chat.revertPopover.revert': '撤回',
+  'chat.revertPopover.fork': '分叉',
+  'chat.revert.toast.undo': '已撤回至 {preview}',
+  'chat.revert.toast.redo': '已重做',
+  'chat.revert.toast.restored': '已恢复全部消息',
   'chat.errorBoundary.title': '聊天错误',
   'chat.errorBoundary.description': '聊天界面发生错误，可能是临时网络问题或消息数据损坏导致。',
   'chat.errorBoundary.sessionLabel': '会话',