`send_message_as_user`'s schema also marks `title` as required, but
`buildChatMessageSendInvocation` only pre-validated it for direct
messages. Sending `dws chat message send --group <cid> --text "1"`
without `--title` therefore reached the API and returned the same
misleading `发群服务窗会话消息失败` business error that #250 fixed for
direct messages, just on the other branch.
Pre-validation now covers both branches: group sends without title
return `--title is required for group messages (--group)`, direct sends
keep the existing `--title is required for direct messages (...)`
message. `Long` help, the `--title` flag description, the first
`Example` line, and `skills/references/products/chat.md` (including the
deeper "drive → chat" workflow example) are realigned to
"群聊与单聊都必填". `internal/helpers/chat_test.go` gains a
`group-without-title` case, and the existing `group` / `positional-text`
success cases are updated to pass `--title`. No API request shape change.
修雨
ed4673e7d2