refactor: move help content out of translations into locale-specific partials

Replace the instructions translation domain with plain HTML files under
templates/backoffice/help/nl/. Each help/*.html.twig is now a locale
dispatch shim that tries the current locale first and falls back to nl,
so adding English (or any other language) is simply a matter of creating
a help/en/ directory with the translated files — no code changes needed.

Removes instructions+intl-icu.nl.xliff.

templates/backoffice/help/quiz_result.html.twig

@@ -1,5 +1,4 @@
-<h6>{{ 'Results'|trans({}, 'instructions') }}</h6>
-<p>{{ 'The table shows the final result per candidate sorted by score. Red rows are the candidates with the lowest score who are at risk of elimination.'|trans({}, 'instructions') }}</p>
-<p><strong>{{ 'Corrections'|trans }}</strong> — {{ 'Corrections are added for bonus points or joker deductions (half points are possible).'|trans({}, 'instructions') }}</p>
-<p><strong>{{ 'Penalty'|trans }}</strong> — {{ 'Penalty is a time penalty in seconds and is taken into account when scores are tied.'|trans({}, 'instructions') }}</p>
-<p>{{ 'Via Prepare elimination you set the screen colours manually and start the elimination sequence.'|trans({}, 'instructions') }}</p>
+{{ include([
+    'backoffice/help/' ~ app.request.locale ~ '/quiz_result.html.twig',
+    'backoffice/help/nl/quiz_result.html.twig',
+]) }}