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>

news/admin.py

@@ -12,7 +12,7 @@ class NewsPhotoInline(admin.TabularInline):
 class NewsAdmin(admin.ModelAdmin):
     list_display = ["title", "club", "status", "visibility", "created_by"]
     list_filter = ["club", "status", "visibility"]
-    search_fields = ["title"]
+    search_fields = ["title", "title_en"]
     raw_id_fields = ["created_by"]
     inlines = [NewsPhotoInline]