Plots: Use new Compact floating window mode for plots opened in new window

[jmcphers]

VS Code 1.100 introduces a Compact floating window mode. This mode hides the editor tab bar:

https://code.visualstudio.com/updates/v1_100#_floating-window-modes

This floating window mode would be a significant improvement over today's plot windows, which include a vestigial editor tab bar.

We should adopt the new Compact floating window mode for plots opened in new windows from the Plots pane.

[juliasilge]

If we do this, let's close https://github.com/posit-dev/positron/issues/10085.

[rodrigosf672]

Verified Fixed

Positron Version(s) : 2026.01.0 build 24
OS Version          : macOS Tahoe 26.1

Test scenario(s)

• Plot opens in new window → uses Compact mode.
• Compact mode → tab bar hidden.
• Setting disabled → plot opens in normal window.
• Multiple plots → each uses Compact mode.
• R/Python plots → all Compact.
• Plot tools (zoom, save, copy) → still work.
• Closing window → returns focus to main editor.
• Compact window respects OS window rules.
• No Assistant status bar in Compact windows.

[rodrigosf672]

Note for new issue

Lock/unlock group does not work