[Feature Request] Setting to open files in existing window as tabs

[iamkartiknayak]

Issue/Description:
Introduce an opt-in setting that allows files to open in the currently active COSMIC Edit window as new tabs instead of spawning a new window. This is especially useful for users running tiling window managers, where automatic new windows can disrupt layouts.

The default behavior can remain unchanged to preserve current workflows. When the setting is enabled, files would open as tabs in the existing window.

Expected Behavior:

• When the opt-in setting is enabled, files open as tabs in the active COSMIC Edit window
• When the setting is disabled, current behavior is preserved

Other Notes:
A modifier action such as Shift + Enter can be used to always opens the file in a new window from COSMIC Files

[cstby]

Given that the text copied to the clipboard doesn't persist after the editor is closed, this seems extra important.