feat(cron): surface last_fire_error on Cron Job records (#925) (#933)

Backend stamps last_fire_error ({at, detail}) on a job when a scheduled fire
can't reach the gateway loopback (gateway down / api_server not bound) —
the "job runs manually but never auto-fires" case. Previously invisible in
mobile.

- CronJob.kt: model as CronJobFireError(at, detail) — the backend sends a
  nested object, NOT a flat string (issue's String? proposal would fail to
  deserialize), plus the last_fire_error field.
- CronJobsScreen: "Fire failed" ERROR badge in the list + "Dispatch Error"
  row (detail + timestamp) in the Run Details dialog.
- Strings en/zh/ko. Test: job with last_fire_error loads + parses.

Backward-compatible: field has a default, existing jobs without it parse fine.

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/main/res/values-ko/strings.xml

@@ -584,6 +584,8 @@
     <string name="cron_edit_field_run_continuity">실행 연속성</string>
     <string name="cron_edit_hint_run_continuity">이 작업의 이전 출력을 매 실행에 주입</string>
     <string name="cron_badge_continuity">연속</string>
+    <string name="cron_detail_dispatch_error">발송 오류</string>
+    <string name="cron_badge_dispatch_error">실행 실패</string>
     <string name="cron_edit_hint_schedule">예: 0 9 * * * 또는 every 2h</string>
     <string name="cron_edit_hint_deliver">예: origin, local, all, 또는 telegram:chat_id</string>
     <string name="cron_edit_hint_skills">한 줄에 하나씩</string>