Fix mismatched fallback text colour on the initials badge/button

The initials badge and reset button hardcoded two independent
fallback literals -- a background (#ec4899 / #0ea5e9) and a text
colour (#ffffff) -- that were only ever chosen together for a club's
own colour via Club._content_color_for. #ffffff on #ec4899 or
#0ea5e9 actually contrasts worse than black by the same WCAG formula
the app already uses elsewhere (verified: 6.4:1 vs 3.3:1, and 7.6:1
vs 2.8:1). Added a contrast_color filter so the text colour is always
derived from whatever background hex is actually in play -- real
club colour or fallback alike -- instead of a second, independently
guessed literal that can silently drift out of sync with the first.

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

static/css/app.css

@@ -4294,6 +4294,9 @@
     --tw-tracking: var(--tracking-wider);
     letter-spacing: var(--tracking-wider);
   }
+  .text-wrap {
+    text-wrap: wrap;
+  }
   .whitespace-nowrap {
     white-space: nowrap;
   }