Keep Bestellnummer/Datum side by side below 500px too

Reverts the col-span-2 full-width-row experiment for very narrow
phones — side by side reads better even with the occasional wrap.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -2146,11 +2146,11 @@ Went through several rounds of visual feedback:
   columns there. The 6 fields in DOM order already tile cleanly into 3
   rows of 2 (Bestellnummer/Datum, Artikel/Status,
   Zahlungsstatus/Gesamtbetrag) without any reordering.
-- Bestellnummer/Datum additionally span both tracks of that 2-column
-  layout (`col-span-2 min-[500px]:col-span-1`) so the long order number
-  doesn't wrap on very narrow phones — but must drop back to
-  `col-span-1` once 4 columns kick in, since spanning 2 of 4 tracks
-  there would push Datum to start at the 3rd column instead of the 2nd.
+- Bestellnummer/Datum deliberately stay at `col-span-1` in both the
+  2-column and 4-column layouts, side by side even below 500px — a
+  brief `col-span-2` experiment (own full-width row each, to avoid the
+  order number wrapping on very narrow phones) was reverted since it
+  read worse than the occasional wrap.
 - Artikel forces `col-start-1` so it wraps to its own row in the
   4-column layout instead of Grid's auto-placement flowing it into the 2
   cells left empty in row 1 after Bestellnummer/Datum (a harmless no-op