feat: add last-turn diff view

Adds a Last turn scope to DiffView that renders OpenCode snapshot diffs from the latest user message summary without re-fetching git contents. The view hides Review in that mode and carries the selected diff scope through main and context-panel navigation.

Connects latest-turn changed-file chips in chat to the snapshot diff view on desktop and mobile, while keeping older turn chips static/read-only to avoid misleading affordances and extra subscriptions. Updates localized labels and empty states plus changelog.

Validation: bun run type-check (packages/ui); bun run lint (packages/ui).

packages/ui/src/lib/i18n/messages/pl.ts

@@ -1537,6 +1537,7 @@ export const dict: Record<I18nKey, string> = {
   'diffView.section.files': 'Pliki',
   'diffView.selector.selectFile': 'Wybierz plik',
   'diffView.state.cleanWorkingTree': 'Drzewo robocze jest czyste, brak zmian do wyświetlenia',
+  'diffView.state.noLastTurnChanges': 'Brak zmian z ostatniej tury do wyświetlenia',
   'diffView.state.failedToLoadDiff': 'Nie udało się wczytać diffu',
   'diffView.state.largeDiff': 'Duży diff ({count} zmienionych linii)',
   'diffView.state.largeDiffDescription': 'Renderowanie może być wolne. Nadal możesz wyświetlić diff przyciskiem poniżej.',
@@ -1548,6 +1549,7 @@ export const dict: Record<I18nKey, string> = {
   'diffView.summary.changedFilesPlural': 'Zmieniono {count} plików',
   "diffView.scope.changed": "Zmienione",
   "diffView.scope.staged": "Staged",
+  "diffView.scope.lastTurn": "Ostatnia tura",
   "diffView.scope.selectorAria": "Wybierz tryb zmian",
   'diffView.summary.changedFilesSingle': 'Zmieniono {count} plik',
   'directoryExplorerDialog.actions.addProject': 'Dodaj projekt',