List queued steers and follow-ups in a pending column above the prompt

[TheGreatAxios]

Summary

• Queued steers and follow-ups list in a transient pending column stacked on the prompt box instead of echoing labelled rows into the transcript; delivery paints an ordinary user row.
• The column is a selection surface: Up/Down select a held row, Enter force-delivers it now (a steer injects into a live turn, otherwise it sends), Ctrl+X drops it, Esc backs out, and a guidance row names the keys. Ctrl+G still pops the newest item into the composer for editing.
• /help lists the new chords; TUI and PRODUCT docs describe the column.

Verification

• bun run lint, bun run typecheck, and bun run build pass
• bun test ./src/tui — 2233 tests pass, including new coverage for the column fold, selection paint, Ctrl+X drop, Enter force-deliver, and steer-inject routing
• Full bun run test has pre-existing sandbox git-subprocess timeouts unrelated to this branch

Fixes CL-7791

[linear-code]

CL-7791