Resize quotation canvas columns and understand column weights

Drag a column boundary to resize that column and its right neighbour as a pair, and learn how the new widths are saved as relative weights.

1. On the quotation canvas, hovering a column boundary shows a col-resize cursor.

2. Dragging a column boundary resizes that column and its immediate right neighbour as a pair.

3. The last column has no right neighbour so it cannot be dragged.

4. On mouse release the new widths are converted back into relative weights and saved on the quotation (an entry per column keyed by its field).

5. Custom widths persist across sessions and exports for that quotation.

6. Each display field ships with a default weight.

7. The first time a column becomes visible its default weight is seeded into the saved set.

8. Column pixel width = (table width / sum of visible weights) x weight.

9. Hiding or showing a column re-flows every other column proportionally.

10. The filler columns visually merge into the last real column so footer labels have room.