Quick-Branch for Pinned Chats

Add a shortcut to branch directly from pinned chats in the sidebar without requiring users to open the chat first.

Pinned chats often serve as templates that users branch from repeatedly. Currently, users must open the pinned chat before clicking the branch button.

This request proposes adding a direct branch option to pinned items in the sidebar, allowing users who maintain template chats (like "Data extraction chat") to create new instances in a single action rather than multiple steps.

A small branch icon could appear when hovering over pinned items, consistent with the existing branch button design.