docs: make the top of the README readable on a phone

The before/after comparison was a raw <table> with width="50%" cells.
GitHub honors that legacy attribute directly, so the two columns lock to
a 50/50 split of a ~340px container instead of letting the table scroll
as one unit. The right cell holds a <pre> block, which does not reflow,
so the half that shows the actual injection payload got crushed into a
~160px strip with a nested scrollbar. Now two stacked sections, correct
at every width, with all wording and the plan-data block preserved.

The stats panel was a 48-column box-drawing block. 48 columns need about
375px of text width, more than any phone has in portrait, and every
value is right-flushed, so the labels rendered and the numbers were the
first thing pushed off screen. A first-time mobile visitor saw five
labels and no numbers. Now a two-column table, content-sized, widest
line 38 characters, and readable by screen readers.

Also documents PWF_PLAN_GUARD, records that the language variants are
real translations that now ship the full script surface, and corrects
the parity count from 18 to 19 (the npm package.json joined the set in
#213). Test suite figure updated to 417.