Add option to disable dead key / preedit indicator in input field

Description

When typing diacritics using dead keys (e.g., pressing ´ then a to produce á), a small colored box appears in the bottom-left corner of the terminal showing the intermediate dead key character. This happens across all terminal emulators (Ghostty, Terminal.app, etc.), confirming it's a Claude Code behavior.

Screenshots

The yellow ´ box appears at bottom-left after pressing the dead key, before the second keystroke completes the character:

This is the preedit/compose indicator rendered by Claude Code's input system.

Request

Add a configuration option (e.g., in settings.json) to hide or disable this preedit indicator. For users with non-ASCII keyboard layouts (Icelandic, French, German, Spanish, etc.) who type diacritics frequently, the flashing indicator on every accented character is distracting.

Environment

• Claude Code: latest channel
• macOS (Apple Silicon)
• Reproducible in: Ghostty 1.2.3, Terminal.app, and likely all terminals
• Keyboard layout: Icelandic (uses dead keys for á, é, í, ó, ú, ý)