Desktop app: add search bar/filter in Settings on macOS

Summary

Add a search bar in the Codex desktop app Settings on macOS so users can quickly find preferences and toggles.

Problem

As the Settings surface grows, it becomes slow to locate a specific option by scanning manually. This is especially noticeable when trying to find rarely used configuration, audio/transcription settings, notifications, MCP/tooling settings, or experimental flags.

Requested behavior

• Add a search field at the top of Settings
• Filter settings sections and individual rows by search text
• Highlight matched labels/descriptions
• Preserve normal keyboard navigation while filtering
• Show an empty state when there are no matches

Why this helps

This would make the desktop app easier to navigate and reduce friction when changing configuration, especially for users with many settings enabled or when troubleshooting.

Platform

macOS desktop app