## Context

Replaces the native system prompt used for "About Zed" with a custom
standalone GPUI window which can open without the need for opening a Zed
editor window of none are currently open.

Closes #49157

## How to Review

Single file change in `crates/zed/src/zed.rs` — the `about` function is
replaced by `open_about_window`. The new window deduplicates itself,
matches the old layout (title, version info, Ok + Copy buttons), and
closes on either button or Escape.

## Screenshots

### Old Behavior

Opening the about window when no other Zed window is open will open a
new empty zed window and display the about window on top:
<img width="1710" height="1072" alt="image"
src="https://github.com/user-attachments/assets/10a22027-4aa8-4cc9-9d91-368d76bb6a91"
/>

### New Behavior

If there is no open Zed window we just open an instance of the new About
window:
<img width="1710" height="1076" alt="image"
src="https://github.com/user-attachments/assets/e55c92dc-18db-4556-83bd-1a78db754eff"
/>


If there is at least one open Zed window, we display the About window on
top of it:
<img width="1710" height="1075" alt="image"
src="https://github.com/user-attachments/assets/a653e402-a107-4b50-8d09-7d50f537b36c"
/>

In bright mode:
<img width="1710" height="1071" alt="image"
src="https://github.com/user-attachments/assets/c72f8856-7152-47a6-a630-0875372a270f"
/>

Additionally, the ESC button will now act like clicking the Ok button
and close the about window without copying its content.

## Self-Review Checklist

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
  - no new tests have been implemented
- [x] Performance impact has been considered and is acceptable

Release Notes:

- Improved the About Zed dialog to open as a standalone window instead
of a native system prompt

---------

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>