[Feature] FleetView: support pasting images into the "start a task in the background" input

Summary

In FleetView (Claude Code CLI background-agents view), the input bar labeled "start a task in the background" does not accept pasted images. In a regular Claude Code chat input I can paste a screenshot (Cmd+V) and it attaches; in the FleetView input, pasting does nothing — no attachment, no preview, no error.

Expected behavior

Pasting an image (Cmd+V from clipboard) into the FleetView input should attach it to the prompt the same way it does in the standard Claude Code session input. The background agent should then receive the image as part of its initial task.

Actual behavior

The paste is silently dropped. No attachment appears, no error, no fallback. I have to either:

• Save the image to disk, then reference a path the agent can read (which doesn't help if the agent has no filesystem access to my screenshot)
• Open a regular Claude Code session, paste there, and then re-create the task in FleetView
• Skip the image entirely and try to describe it in words

Why this matters

A lot of background tasks I want to fan out start from a screenshot — UI bug to investigate, design mock to implement, dashboard reading to interpret. Forcing me to round-trip through another surface to get the image in defeats the "kick it off and walk away" ergonomics of FleetView.

Environment

• Surface: FleetView (Claude Code CLI background agents view) — the "start a task in the background" prompt bar
• Platform: macOS (Darwin 25.4.0)
• Terminal: Ghostty