[LOW] Ghost preview hides all real cards when terminal fits exactly one card slot

When visibleSlots() returns 1 (the minimum, enforced by the max(..., 1) guard), slots-- drives it to 0. The subsequent computation then becomes:

scroll = max(len(cards)-0, 0)  // = len(cards)
end    = min(len(cards)+0, len(cards))  // = len(cards)

The render loop (for i := scroll; i < end) is empty, so every real card disappears and the column shows only header + rule + "… N more" + ghost. On a tall-enough terminal this never triggers (slots ≥ 2), but on a constrained terminal where only one card row fits, a drag-over causes the entire card list to vanish except the ghost.

A simple guard avoids the underflow:

if slots > 1 {
    slots--
    scroll = max(len(cards)-slots, 0)
}

That way a one-slot terminal still renders its single real card and skips the ghost, matching the PR description's intent ("terminals too small to show even one real card get a … N more line").

[LOW] Dropping idx != m.selCol lets dropTarget override the selected column's white border with green

The old condition was:

case m.dragging && idx == m.dragCol && idx != m.selCol:

The new dropTarget is:

m.dragging && idx == m.dragCol && !containsCard(cards, m.dragCardID)

There is no longer a guard preventing dropTarget from being true when the destination column is also the selected column (m.dragCol == m.selCol). Because case dropTarget: appears first in the border-color switch, a drag toward a column the user previously selected will show a green border instead of the white one they'd normally see.

This may well be intentional — the green ghost+border is more informative during a drag — but since the removal is silent and the old guard was explicit, it's worth a quick confirmation that this is the desired UX before merging.