Fix Ctrl+Shift+C in wezterm clobbering zellij clipboard (flakes-5oyz)

Copy (to system clipboard) doesn’t work when using wezterm → incus shell → zellij. Root cause: Ctrl+Shift+C runs CopyTo(‘Clipboard’) which copies empty terminal selection, overwriting what zellij put in clipboard via OSC 52. Fix: only copy when there’s an actual selection.

Summary of Changes

Changed binding in from a direct action to a callback that first checks if there’s an actual terminal selection. Only copies when selection is non-empty, matching kitty’s behavior and preventing the clipboard from being clobbered when zellij has already set it via OSC 52.