Replace the hardcoded 4-option deliver dropdown (local/discord/telegram/slack)
with a dynamic select populated from a new GET /api/crons/delivery-options
endpoint that reads _KNOWN_DELIVERY_PLATFORMS from hermes-agent.
Key changes:
- Add GET /api/crons/delivery-options endpoint returning all known platforms
- Frontend loads options asynchronously on first cron form open, with caching
- Enable deliver editing for existing jobs (was previously disabled)
- Include deliver in update payload when editing cron jobs
- Fallback to local-only if API unavailable
- Custom deliver values (e.g. feishu:oc_xxx) shown with * suffix
- Add cron_deliver_custom i18n key to all 12 locales
- Add 5 integration tests for the new endpoint