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/es.ts

@@ -1220,6 +1220,7 @@ export const dict: Record<I18nKey, string> = {
   "diffView.state.loadingRepositoryStatus": "Cargando estado del repositorio...",
   "diffView.state.notGitRepository": "No es un repositorio Git. Usa la pestaña Git para inicializar o cambiar de directorio.",
   "diffView.state.cleanWorkingTree": "Worktree limpio, no hay cambios para mostrar",
+  "diffView.state.noLastTurnChanges": "No hay cambios del último turno para mostrar",
   "diffView.state.failedToLoadDiff": "No se pudo cargar la diferencia",
   "diffView.state.loadingDiff": "Cargando diff...",
   "diffView.state.loadingChanges": "Cargando cambios...",
@@ -1229,6 +1230,7 @@ export const dict: Record<I18nKey, string> = {
   "diffView.summary.changedFilesPlural": "{count} archivos modificados",
   "diffView.scope.changed": "Cambiados",
   "diffView.scope.staged": "Staged",
+  "diffView.scope.lastTurn": "Último turno",
   "diffView.scope.selectorAria": "Seleccionar modo de cambios",
   "diffView.actions.retry": "Volver a intentar",
   "diffView.actions.renderAnyway": "Renderizar de todos modos",