[Feature Request] Add configurable TUI scrollback buffer size for conversation history

Bug Description

Problem

Claude Code's TUI uses an alternate screen buffer, which means the terminal's own scrollback settings don't apply. When Claude outputs large amounts of code, diffs, or tool results,
earlier parts of the conversation quickly become unreachable by scrolling up.

The current scrollback is very limited and there's no way to configure it.

## Expected behavior

A configurable setting (e.g., scrollback_lines or max_display_lines) to control how much conversation history remains accessible when scrolling up in the TUI.

## Workarounds tried

• Terminal scrollback settings (irrelevant — alternate screen buffer)
• Ctrl+O to collapse blocks (helps but doesn't solve the core issue)
• /compact to shorten conversation (loses context)

## Environment

• Claude Code v2.1.89
• macOS Terminal.app (but applies to any terminal since it's the TUI's own buffer)

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 2.1.89
• Feedback ID: 2e44c785-ff90-429c-8b2e-4edae3e4cf8a

Errors

[{"error":"Error: NON-FATAL: Lock acquisition failed for /Users/tom/.local/share/claude/versions/2.1.89 (expected in multi-process scenarios)\n    at ux_ (/$bunfs/root/src/entrypoints/cli.js:1891:2138)\n    at xU6 (/$bunfs/root/src/entrypoints/cli.js:1891:1218)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-02T09:33:32.574Z"},{"error":"McpToolCallError: Error: AppleScript error: 47:63: execution error: Aplikace „Reminders“ obdržela chybu: „list \"Reminders\"“ nelze načíst. (-1728)\n\n    at bZ9 (/$bunfs/root/src/entrypoints/cli.js:1585:63)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-02T11:06:10.741Z"}]