The cron delivery table only showed Discord/Telegram with explicit
target syntax and described Slack and every other platform as
home-channel-only. In fact the generic platform:<target> routing in
_resolve_single_delivery_target resolves explicit targets for every
platform: Slack (#channel / channel ID / channel:thread_ts), Matrix
(room/user IDs), Feishu (chat:thread), WhatsApp (JID / E.164), Signal
(group / E.164), SMS, Email, and Weixin all have dedicated explicit-
target branches in _parse_target_ref; the remaining platforms accept a
generic platform:<chat_id> passthrough.
Update the Delivery Model table (en + zh-Hans) to show the real
per-platform syntax, document #channel name resolution via the channel
directory, and note the Slack thread_ts nuance. Docs-only.
e1f4098b9f