R8.1: document content keeps the file's colours in a dark app

Pages, cells, slides and PDF pages paint as the file says in any
appearance; only the chrome around them follows dark mode. The
kernel keeps Ely's one light scheme, sent once a view, and MuPDF
no longer inverts. Reviews now run gpt-6.1-sol at xhigh.

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

tests/scripts/theme.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# ElyTable's grid follows the app's dark and light mode.
+# ElyTable's cells stay white in dark and light mode.
 set -euo pipefail
 
 root=$(cd "$(dirname "$0")/../.." && pwd)
@@ -46,6 +46,6 @@ check dark "$(shade_of dark)"
 dark=$shade
 check light "$(shade_of light)"
 light=$shade
-[ "$dark" -lt 80 ] || fail "the dark grid paints at $dark"
-[ "$light" -gt 200 ] || fail "the light grid paints at $light"
+[ "$dark" -gt 200 ] || fail "the dark app's grid paints at $dark"
+[ "$light" -gt 200 ] || fail "the light app's grid paints at $light"
 echo "ok: theme (dark $dark, light $light)"