feat: show model in working indicator and fix streaming bottom jitter

- Working indicator shows provider icon and model name with the live
  status (e.g. 'Fable 5 is reading file'), localized via
  chat.statusRow.modelStatus
- Pin auto-follow to the exact fractional scroll maximum and re-pin on
  every passive follow instead of skipping within tolerance
- Round message text line-height to whole pixels so streamed content
  grows on the pixel grid; kills the 1px vertical jitter of
  bottom-anchored rows during streaming

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

@@ -1775,6 +1775,7 @@ export const dict: Record<I18nKey, string> = {
   "chat.statusRow.todo.priority.low": "Prioridad baja",
   "chat.statusRow.actions.stopGeneratingAria": "Detener la generación",
   "chat.statusRow.tasksTitle": "Tareas",
+  "chat.statusRow.modelStatus": "{model} · {status}",
   "chat.statusRow.summary.activeLeft": "{active} activas · {left} restantes",
   "chat.statusRow.aborted": "Interrumpido",
   "chat.revertIndicator.redo": "Rehacer",