capabilities ant/term ↗

feat: kitty graphics relative placements and under-background z-index P=/Q=/H=/V= position a placement against another one instead of the cursor: the parent may be an anchored placement, another relative one (up to RELATIVE_MAX_DEPTH, ETOODEEP beyond), or a virtual placement, which sits at the top-left of the placeholder cells showing it. Positions are resolved per frame from the parent, so children follow scrolling and a re-placed parent; ENOPARENT/ECYCLE/EINVAL are reported at creation, deleting a parent deletes its relatives (and an image left with no placement), and the sweep drops orphans. Placements below INT32_MIN/2 draw under non-default cell backgrounds but over the default one: the background pass splits in two around them, only when such an image is on screen. Visible placements are now computed once per frame and shared by the image passes.