docs(ui): update help assets and regenerate help pdf

scripts/build_help_pdf.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env sh
+# Build docs/help.pdf from docs/help.md.
+# Requires: pandoc, chromium (headless print-to-PDF).
+set -eu
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+# HTML next to docs/help.md so relative image paths (e.g. images/help/*.svg) resolve.
+HTML="$ROOT/docs/.help-print.html"
+trap 'rm -f "$HTML"' EXIT
+
+pandoc "$ROOT/docs/help.md" -s \
+  --css="$ROOT/scripts/help-pdf.css" \
+  --metadata title="LED controller — user guide" \
+  -o "$HTML"
+
+chromium --headless --no-sandbox --disable-gpu \
+  --print-to-pdf="$ROOT/docs/help.pdf" \
+  "file://${HTML}"
+
+echo "Wrote $ROOT/docs/help.pdf ($(wc -c < "$ROOT/docs/help.pdf") bytes)"