Add a possibility to disable Hover Cards / Popovers

[realsergii]

T3 Code is great! It became my main tool for driving agents. The only thing that annoys me is Hover Cards / Popovers that appear when I move my mouse between the sidebar and the main area. All of them are visual clutter to me and make the tool feel less professional. All I need is a switch to enable/disable them. That would make my experience night and day better.

[realsergii]

BTW, my usage pattern is - very long-lived threads (could easily be 1 month or more). It's not like a thread per PR -> settle. Maybe that's why I see so much clutter most other users don't see.

[realsergii]

I narrowed this down and opened #24906 with a focused version.

Scope: one setting, Settings → Appearance → Hover previews, on by default. When it's off, the sidebar thread card, the subagent cards and the timeline minimap message preview don't render. Ticks, click-to-jump, keyboard navigation and button tooltips work as before.

The main trigger turned out to be the timeline minimap. It sits on the chat's left edge, so moving from the sidebar into the chat hovers it. In long threads the ticks are dense, so it fires on almost every crossing.

If this scope looks right to a maintainer, a quick 👍 here would let me link it as approval in the PR. I'm happy to adjust the setting name or placement.