Setting to auto-pin newly created chats in the agents view

Summary

Add a setting (e.g. fleetView.autoPinNewSessions: true in settings.json) that automatically pins every newly-created chat in the claude agents (FleetView) view, so new sessions appear in the top "Pinned" section instead of being grouped under their directory below.

Motivation

In the agents view today, new chats land inside the per-directory listings (e.g. ~/Desktop 15, ~/Desktop/abi 7). To get to a chat I just spawned, I have to drill into its directory and find it among N siblings. The Pinned section at the top is where my eyes already go, but it requires a manual pin step per chat.

For users who run many concurrent agents and use the Pinned section as their working set, "new chat = pinned" matches the mental model: recently-started chats are the ones I actively care about.

Proposed behavior

• New setting: fleetView.autoPinNewSessions (bool, default false).
• When true, every new chat is created with pinned=true and appears at the top of the Pinned section.
• Pinning remains user-controllable — unpin/repin still works as today.
• Optional refinement: fleetView.autoPinNewSessions: "background" to only auto-pin chats started from the "start a task in the background" input.

Related

• #22617 — broader project/folder organization with manual pin keybind.
• #46474, #55291 — manual pin/star (closed, shipped).
• #59087 — Cowork artifacts auto-pin is unwanted — shows the default-pin axis is configurable elsewhere; same lever, opposite side.