[FEATURE] Pin prompt/composer box to bottom of terminal pane (CLI TUI)

Preflight

• [x] Searched existing issues; no exact match for pinning the input/composer region to the terminal bottom
• [x] Single feature request

Problem Statement

In long Claude Code CLI sessions, the conversation transcript and tool output dominate the terminal. When I scroll up to read earlier messages, command output, or diffs, the prompt/composer input area is not anchored to the bottom of the viewport. I have to scroll back down to see what I’m typing or to access controls (model, permissions, queue, etc.).

This hurts everyday workflows:

• Reviewing prior context while composing the next message
• Debugging with lots of bash/tool output above the input
• Using split or short terminal panes where vertical space is scarce

Related pain exists around scroll behavior (#25042, #826) but this request is specifically about layout: a fixed bottom input region with scrollable history above.

Proposed Solution

Add a TUI layout mode (preferably default-on) that pins the composer/prompt box to the bottom of the terminal pane:

1. Fixed bottom band for the input UI (multiline prompt, shortcuts, mode indicators).
2. Scrollable transcript region above for messages, tool use, and stderr/stdout — only this area scrolls.
3. No occlusion: pinned chrome must not cover the last lines of transcript; use a visible separator and/or reserve explicit row count.
4. Configuration (example):

{
  "tui": {
    "pinComposerToBottom": true,
    "composerMinRows": 3
  }
}

Optional: pin a slim status/footer row directly above the composer (cwd, model, context %, cost).

Alternative Solutions

• Manually resizing the terminal and relying on auto-scroll — does not keep input visible when reading history.
• Running Claude Code in a separate tmux pane for input only — awkward, loses integrated approvals and UI hints.
• Desktop app chat pane — not available when using headless/SSH/remote dev on CLI only.

Priority

High — meaningful daily productivity impact for terminal-first users.

Environment

• OS: macOS (Darwin 25.4.0)
• Interface: Claude Code CLI / TUI

Additional context

Parity with IDE-style agent UIs (e.g. Cursor composer) where the prompt stays fixed at the bottom while content scrolls above. Willing to help validate UX or provide recordings.