[a-team-app]

Summary

Ctrl+Shift+T (also uct, and File › Undo close tab after Close all tabs) reopens the file tab you closed most recently. It comes back in the same group and slot in the tab strip as the active tab, with the cursor and scroll where they were. Ctrl+Z and redo pick up where they left off, as long as the file on disk still holds what the tab had when it closed. Press it again to bring back the next one. After Close other tabs or Close all tabs, repeated presses bring the tabs back one at a time, in their original order.

Closes #578

Notes

• The tab close button criterion: TG's Tabs draws no close button on a tab, so TuiCode has none. Every way a file tab closes goes through EditorGroup.Close, and that is where tabs are remembered, so a close button added later would count with no extra work.
• A tab from a second group that has gone (e.g. after Close all tabs with a split) reopens at the end of the first group. Its old index belonged to the other group's strip, so it means nothing in the first.
• The F1 Tabs row, like every F1 row, appears only while the command is enabled, so it shows once something has been closed. With nothing to reopen, the item is dimmed in the menu and left out of the palette.
• Up to 20 closed tabs are kept per session. Switching folders or quitting forgets them.

a-team try tuicode 580

[a-team-app]

CI broke because main is red, not because of this PR. #581's UnsavedEditsHostTests still used ConfirmView, which #582 removed. I merged main in and switched that test to ConfirmDialogs.Choose(..., "Don't save") (5a0138d). Merging this PR fixes main as well.

[a-team-app]

CI failed on UnsavedEditsTests.A_renamed_file_takes_its_copy_with_it, which came from #581 and not from this change. The test counted recovery copies before the next session's background write had finished, so it sometimes saw a leftover .tmp. Fixed in 1ea30a7 by waiting for that write, as Recovering_takes_over_the_copy already does.