## Summary

macOS 27 Beta delays clicks in titlebar regions while AppKit determines
whether a gesture should become a drag, single click, or double click.
Zed's main workspace windows render a custom titlebar that already
handles window movement via `Window::start_window_move`, so they do not
need AppKit's native movable-titlebar behavior.

This sets `is_movable` to `false` for the main `MultiWorkspace` windows
and documents the `WindowOptions::is_movable` caveat for GPUI users with
custom titlebars.

## Background

The previous fix for this, #58947, used AppKit's private
`_opaqueRectForWindowMoveWhenInTitlebar` SPI to mark GPUI's full-size
content view as app-owned titlebar content. That fixed delayed titlebar
clicks, but was later reverted in #59214 because it also affected
windows that rely on AppKit's native titlebar dragging, like the
settings window.

This PR takes a narrower approach by only changing Zed's main
custom-titlebar windows. Those windows already implement dragging
explicitly via `Window::start_window_move`, so disabling AppKit's native
movable-titlebar behavior fixes the macOS 27 Beta click delay without
affecting other window types.

Release Notes:

- Fixed delayed clicks in the custom titlebar on macOS 27 Beta.