Make pending attachment removal discoverable

[ShaanNarendran]

Problem

After attaching an image, the TUI displays the pending attachment but does not show how to remove it. /attach clear works, but users must discover or guess that command.

Desired outcome

Show a removal hint or interactive action next to pending attachments. Possible approaches include:

• displaying /attach clear in the attachment bar;
• providing a keybinding to remove the latest or all attachments;
• exposing removal through an attachment picker or context action.

A user should be able to discover the removal flow without consulting documentation.

Compatibility and security impact

This is a client-side interaction improvement. Blob transport and daemon ownership should remain unchanged.

Issue tracking

Axl issue mirror: #35 | GitHub #35