Docs / UX: what's the difference between "queued" and "pending" messages?

## Summary
The CLI surfaces two distinct concepts — "queued" messages and "pending" messages — without explaining how they differ. From the user's perspective they look like the same thing (a message you've typed but the agent hasn't processed yet).

## Questions to resolve
- Is there a meaningful behavioral difference (lifecycle, when each is flushed, when each can be cancelled)?
- If yes: please document it in `/help` and in the on-screen labels (e.g. tooltip on the queue indicator).
- If no: please unify the terminology to a single word in the UI.

## Why this matters
Existing issues about queued-message editing/cancellation (#2055, #2378, #2905, #1857, #3692) all use "queued"; some other surfaces use "pending." Users can't tell whether they're filing duplicate reports about the same thing or two genuinely different bugs.

首先比较 CLI 中对 "queued" 和 "pending" 的使用，然后检查 /help 文本以及 issue 中提到的屏幕队列指示器标签。确定这些术语描述的是不同的生命周期、刷新行为还是取消状态；在 /help 和 tooltip 中记录这种区别，或者如果它们含义等同，则统一术语。

由索引模型根据 Issue 内容生成。