Feature Request: Add setting to hide the recent sessions list in the Chat panel

The Chat panel currently always shows the top 3 recent sessions at the top, regardless of whether the user wants them there. This permanently consumes vertical screen space and creates visual clutter.

There is already a dedicated button to access previous sessions on demand — that's the right pattern. The always-visible sessions list on top of that is redundant for users who don't need it.

**Request:** Add a VS Code setting (e.g. `chat.showRecentSessions`) to let users hide the recent sessions list from the Chat panel. No change to default behavior — users who find it useful keep it; users who don't can turn it off.

The underlying session history management doesn't need to change at all. This is purely a UI visibility preference.

*(Screenshot below — will be attached)*