Round out referee amounts/colors, and add bilingual (nl/en) news content

Referee display: drop the redundant "External" pill from the PDF form, round
the event/dashboard "due" summary to 2 decimals (a fine-grained km rate like
0.083 was pushing the raw total to 3+ decimals), and theme the PDF's accent
colors off the club's own primary/secondary colors instead of a hardcoded
default.

News: title/body stay the club's own-language (Dutch) text; new optional
title_en/body_en carry a translation, with News.effective_title_en/
effective_body_en resolving the fallback to the original on read rather than
copying it in at save time -- so editing the Dutch text later never leaves a
stale English copy behind, and existing rows get correct fallback behaviour
with no backfill. The news form lays both languages out side by side; the
detail page only shows an English section when one was actually added. The
public API returns both languages in one call (title_nl/body_nl/excerpt_nl
alongside title_en/body_en/excerpt_en, the latter never blank) -- a breaking
rename of the previously-unprefixed title/body/excerpt fields.

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

management/templates/management/news_detail.html

@@ -41,6 +41,16 @@
         </div>
     </div>
 
+    {% if news_item.title_en or news_item.body_en %}
+        <div class="card bg-base-100 shadow mt-4">
+            <div class="card-body">
+                <h2 class="card-title text-base">{% trans "English" %}</h2>
+                {% if news_item.title_en %}<p class="font-semibold">{{ news_item.title_en }}</p>{% endif %}
+                {% if news_item.body_en %}<p class="whitespace-pre-line">{{ news_item.body_en }}</p>{% endif %}
+            </div>
+        </div>
+    {% endif %}
+
     <div class="card bg-base-100 shadow mt-4">
         <div class="card-body">
             <div class="flex items-center justify-between">