Redesign claim-approved and password-reset emails as branded HTML

Confirmed Resend's /emails endpoint accepts an html field alongside
text. Claim-approved email now carries an HTML alternative with the
club's logo/colours; allauth's password-reset email is overridden
with the same treatment, falling back to RosterChief's own branding
outside a club context.

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

club/templatetags/club_email.py

@@ -0,0 +1,25 @@
+"""Template helper shared by every HTML email that shows a club's logo.
+
+An <img> in an email has no page to resolve a relative /media/... URL against
+the way a browser tab would -- the inbox fetches it cold. Storage backends that
+already return an absolute URL (e.g. S3 in production) are unaffected; this
+only matters for the local FileSystemStorage used in dev, where FieldFile.url
+is relative.
+"""
+
+from django import template
+
+register = template.Library()
+
+
+@register.simple_tag(takes_context=True)
+def absolute_media_url(context, file_field):
+    """An absolute URL for ``file_field`` (e.g. ``club.logo``), for use in an
+    email. Falls back to the field's own (possibly relative) ``.url`` when
+    there's no request in the template context to build an absolute one from --
+    better a relative URL than a hard error while rendering the email."""
+    if not file_field:
+        return ""
+
+    request = context.get("request")
+    return request.build_absolute_uri(file_field.url) if request is not None else file_field.url