Components.AI: Render and manage pending follow-up messages

### Is your feature request related to a problem? Please describe the problem.

Pending follow-ups need a visible, stable UI outside the composer while an answer is streaming.

### Describe the solution you'd like

Render ordered pending messages at the end of the conversation, outside the composer, with an individually accessible remove action and clear distinction from already-dispatched messages.

### Additional context

Leaf task for #68227 requirement C11. Depends on queue state and stable message identity.

Start from the Components.AI implementation and requirement C11 in issue #68227, then trace the queue state and stable message identity used during streaming. Confirm where conversation messages are rendered and how removal actions are exposed. Done means pending follow-ups appear in order outside the composer, remain distinct from dispatched messages, and each has an accessible remove action.

Written by the indexing model from the issue text.