Table row heights ignore post-shrink column widths

Split out of #126, which fixed this bug class for flex rows. Tables have the same problem in spirit, in two places.

Row heights use unwrapped cell sizes. layoutTable shrinks auto columns proportionally when the table is wider than its container (internal/layout/table.go, step 3), but then computes row heights from each cell's unwrapped IntrinsicSize (step 4). A cell whose text wraps after column shrinking gets a row that is too short, so the wrapped lines are clipped. The fix shape mirrors #126: measure each cell with HeightForWidth(assignedColumnWidth) once column widths are final.

HeightForWidth has no table branch. calculateNode guards tables out of the flex pre-sizing pass and dispatches them to layoutTable, but Element.HeightForWidth does not, so a <table> (default direction Row) falls into the row-container branch and runs flex distribution over its <tr> children during measurement. This is masked today because min-width:auto makes the distribution a no-op and the result lands near the intrinsic estimate, but the measurement should delegate to TableIntrinsicSize (and, once the first item is fixed, to wrap-aware row heights).