gui: Add keyboard shortcuts to history browser tree

[polucifier]

Description

This Pull Request implements the requested keyboard shortcuts for the history browser tree, improving accessibility and overall user experience. Users who prefer using the keyboard over context menus can now manage their command history much faster.

Key Changes

• Added Ctrl + C shortcut to copy the selected command to the clipboard.
• Added Ctrl + D and the Delete key shortcuts to remove the selected command from the history log.
• Added Enter and Return key shortcuts (including the numpad) to mimic the double-click behavior.
• Added safety checks to ensure these shortcuts only trigger on command nodes (COMMAND), preventing accidental modification or deletion of day/time period header nodes (TIME_PERIOD).

Related PRs / Issues

• Follow-up enhancement suggested in gui: Add Copy command feature on right-click to GUI History panel #4927 (specifically addressing the request for accessible keyboard shortcuts like Ctrl+C and Ctrl+D).

How to Test

1. Open the History tab in the GRASS GUI.
2. Select any successfully executed command.
3. Press Ctrl + C and try pasting it into a text editor to verify it was copied.
4. Press Delete or Ctrl + D on a command, confirm the dialog, and verify it was removed.
5. Try pressing these keys on a date header (e.g., "Today") and verify that nothing happens.