Feature request: configurable height/row count for the inline agents tray

## Feature request

Make the inline agents tray (the compact strip above the status line that lists running subagents, e.g. `main` / `codex-planner Critique coin-concurrency plan`) configurable in height / visible row count.

## Problem

When Claude Code runs in a short terminal panel (e.g. the VS Code / Cursor integrated terminal at typical bottom-panel height), the inline agents tray only shows one or two rows — or disappears entirely. With several subagents running in parallel, there is no way to see all of them at a glance:

- Pressing `←` opens FleetView, but that is a modal overlay that replaces the conversation view — you cannot watch agents and the chat at the same time.
- Enlarging the terminal panel shows more tray rows, but sacrifices editor space, which defeats the purpose of a compact bottom panel.

## Proposal

Any of these would solve it:

1. A settings.json key (e.g. `agentTrayRows` or `agentTrayHeight`) to pin the tray to N rows regardless of terminal height, letting the conversation area shrink instead.
2. A bindable keyboard action (e.g. `app:toggleAgentTray` / `app:expandAgentTray`) to expand/collapse the tray inline without entering the FleetView overlay.
3. Making the tray area mouse-resizable in the fullscreen TUI.

## Environment

- Claude Code (fullscreen TUI, `"tui": "fullscreen"`) inside the Cursor integrated terminal
- Windows 11
- Verified against the current settings schema and keybindings action list: no existing option controls this.

Start with the current settings schema and keybindings action list, which the report says were checked, then trace the inline agents tray and FleetView behavior in the fullscreen TUI. Decide which proposed control is in scope and verify that the tray can show the configured rows or expand inline without replacing the conversation view.

Written by the indexing model from the issue text.