Upstream Pi's deleteKittyImage/deleteAllKittyImages return unwrapped control
sequences; legacy callers such as pi-sprite wrap tmux passthrough themselves.
Aliasing OMP's auto-wrapping encodeKittyDeleteImage (and hand-wrapping
deleteAllKittyImages) double-wrapped under tmux, so the outer terminal dropped
the delete command. Match the upstream bare-sequence contract and pin it in
the regression test.