Feature/migrate im channel cronjob from ace

[liukewia]

Summary

Improve LightClaw/ACE → Octop backup restore so IM channels, cron jobs, login sessions, and DB schema come back correctly without a full process restart.

• After restore, rehydrate runtime in-process: reload enabled IM channels from DB (Gateway.reload_channels_from_db) and user cron jobs (CronManager.reload_from_db), while keeping system jobs (e.g. TLS auto-renew) and built-in dashboard/cli channels.
• On migration restore (preserve_users), capture and restore the live JWT secret with users so outstanding browser sessions stay valid; only seed a new secret when none existed.
• Re-run DB migrations after restore so older / LightClaw exports (e.g. schema v1 missing later columns like cron_jobs.mcp_servers) are upgraded on the live pool.
• Parse cron weekday fields with Unix crontab semantics (0/7 = Sunday) so migrated schedules schedule correctly under APScheduler 3.
• Log original English OctopError messages for 5xx responses (app exception handler + JWT middleware) for diagnosis in ~/.octop/logs.
• Minor zh locale fix for presetProviders.

Target branch

• Base is develop (feature / fix — default)
• Base is main (release/* or hotfix/* only)

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation
• Refactor / chore
• Release / hotfix

Test plan

• make all passes locally
• Added/updated tests
  • uv run pytest tests/unit/api/test_backup_restore_rehydrate.py tests/unit/backup/test_snapshot.py tests/unit/backup/test_system_archive.py tests/unit/cron/test_cron_manager.py tests/unit/cron/test_cron_trigger.py tests/unit/gateway/test_gateway_runtime_status.py tests/unit/api/test_exception_handlers.py -q
  • Restore a LightClaw/ACE migration archive with channels + cron jobs; confirm channels reconnect and cron schedules fire without restart
  • Confirm login sessions remain valid when preserve_users / migration restore preserves JWT
  • Confirm numeric weekday cron expressions (e.g. 0 / 7 = Sunday) match Unix crontab behavior

Checklist

• Updated CHANGELOG.md (if user-facing)
• README / docs updated (if needed)