feat(cron): support comma-separated multi-target deliver values

[LLQWQ]

Summary

Allow cron jobs to deliver output to multiple platforms simultaneously by specifying comma-separated deliver values.

Motivation

Previously extracted from #10091 (weixin live adapter PR) but deferred to Batch 4 per #11571. This is a standalone extraction of just the cron multi-target delivery feature.

Usage Examples

• deliver: feishu,weixin — deliver to both Feishu and Weixin home channels
• deliver: telegram:channel1,discord:channel2 — deliver to specific channels on multiple platforms
• deliver: origin,weixin — deliver to origin chat AND Weixin home channel

Changes

• Split _resolve_delivery_target into _resolve_single_delivery_target (handles one platform) and _resolve_delivery_targets (parses comma-separated list)
• _resolve_delivery_target remains as backward-compatible wrapper
• _deliver_result now loops over all resolved targets, collecting errors rather than failing fast
• Duplicate targets are deduplicated by (platform, chat_id, thread_id)

Testing

• tests/cron/test_scheduler.py delivery tests: 26 passed

Closes #11602

[alt-glitch]

Note: #11594 (Batch-4 salvage) is already merged and included multi-target deliver. This PR may be redundant — verify whether the feature already landed via #11594.

[teknium1]

Thanks for the contribution! This feature has already landed on main via a prior merge, so this PR is redundant.

Automated hermes-sweeper review.

• _resolve_single_delivery_target (line 150), _resolve_delivery_targets with comma-split + deduplication (line 234), and the multi-target loop in _deliver_result (line 311) are all present in cron/scheduler.py on current main.
• The implementation was introduced by commit 5ca52bae5 (fix(gateway/weixin): split poll/send sessions, reuse live adapter for cron & send_message, 2026-04-16) — one day before this PR was filed.
• @alt-glitch also noted that PR fix(cron+weixin): Batch-4 salvage — origin fallback dict + Weixin session split + multi-target deliver #11594 (Batch-4 salvage) already included this feature.

The feature you implemented matches what is on main in both structure and behavior. No further action needed here.