Codex 多项改进：长线程、悬停导航、设置搜索等

Tons of improvements landed in Codex.

• Handles super long threads smoothly. - Hoverable navigation rail for previewing and jumping between turns that feels just right. - Settings search covers more controls, with clearer appearance and host-filtering options and easier-to-find custom-provider settings. - Zoom-level changes no longer misalign tooltips, dialogs, menus, selection bubbles, drag previews, or autocomplete. - Copying into Slack preserves Markdown formatting such as bullets, bold text, code, and links; and large text pastes no longer freeze the UI. - And most importantly: a dedicated Pets panel.