Desktop Code tab: superseded prompt text overlaps the active input box instead of stacking above it

Summary

Related to #95896, but a distinct defect: the struck-through "superseded prompt" text and the active input box are drawn in the same space, stacked on top of each other, instead of occupying separate rows. The struck-through text passes behind/through the bordered input box, so the two strings are interleaved and neither is cleanly readable.

Even with the overflow bug in #95896 fixed (wrapping + clipping), this overlap would remain: the superseded text is positioned as an overlay in the composer's own box rather than as its own block above the input.

Expected

The superseded/queued prompt should render as its own row (or chip) above the input field, like the attachment and PR chips do, with the active input below it and no z-overlap.

Environment

• Claude desktop app 2.2553.1 (macOS 26.5.1), Claude Code CLI 2.1.278