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/en.ts

@@ -1402,6 +1402,19 @@ export const dict = {
   'chat.statusRow.tasksTitle': 'Tasks',
   'chat.statusRow.summary.activeLeft': '{active} active · {left} left',
   'chat.statusRow.aborted': 'Aborted',
+  'chat.revertIndicator.redo': 'Redo',
+  'chat.revertIndicator.redoAria': 'Redo — restore reverted messages',
+  'chat.revertPopover.title': 'Reverted',
+  'chat.revertPopover.noTextContent': 'No text content',
+  'chat.revertPopover.forkFromHere': 'Fork from here',
+  'chat.revertPopover.forkFromMessage': 'Fork from this message',
+  'chat.revertPopover.restoreAll': 'Restore all',
+  'chat.revertPopover.restore': 'Restore',
+  'chat.revertPopover.revert': 'Revert',
+  'chat.revertPopover.fork': 'Fork',
+  'chat.revert.toast.undo': 'Reverted to {preview}',
+  'chat.revert.toast.redo': 'Redone',
+  'chat.revert.toast.restored': 'Restored all messages',
   'chat.errorBoundary.title': 'Chat Error',
   'chat.errorBoundary.description': 'The chat interface encountered an error. This might be due to a temporary network issue or corrupted message data.',
   'chat.errorBoundary.sessionLabel': 'Session',