Add messages from the queue editor and pause dequeueing while it is open

Describe the feature or problem you'd like to solve

The queue editing dialog (Ctrl+X, then Q) should behave as a stable place to manage the pending queue. Two related gaps currently make that difficult:

1. There is no Add action for composing and appending a new message without leaving the dialog.
2. Queued messages can be delivered while the dialog is open, so an item may disappear while the user is trying to edit, reorder, or remove it.

Opening the dialog communicates an intent to modify the queue. Processing messages out from under that editing attempt makes the displayed queue a moving target and can cause the agent to act on a message before the user finishes changing it.

Proposed solution

Treat an open queue editing dialog as a temporary hold on dequeueing, and add an Add action to the dialog:

• Add opens a message composer. Submitting it appends the new message to the queue; cancelling leaves the queue unchanged.
• While the dialog is open, the agent may finish its current in-flight work, but it must not deliver the next queued message.
• Closing the dialog releases the hold and resumes queue processing in the resulting order.

These belong in one feature request because they define one UX contract: the queue remains stable and fully editable for the lifetime of the queue editing dialog.

Example prompts or workflows

1. While the agent is working, open the queue dialog, choose Add, compose another follow-up, and append it without leaving the dialog.
2. Open the dialog just before the current turn finishes; the next queued message remains pending instead of being delivered while it is being edited.
3. Reorder, edit, or remove several queued messages while the current work completes; the visible list stays stable until the dialog closes.
4. Add and rearrange messages, then close the dialog; processing resumes using the final queue contents and order.

Additional context

This is intentionally one request rather than two: adding messages and pausing dequeueing are complementary parts of making the queue dialog a reliable editing surface.

Start at the queue editing dialog opened with Ctrl+X, then Q, and trace its message-composer and dequeue-processing entry points. Done means the dialog can add or cancel a message, the next queued message remains pending while it is open, and processing resumes with the final queue order after closing.