Fix the referee PDF's card background, make locations searchable, and add game end times to the API

Referee PDF: the info-card background used CSS color-mix(), which WeasyPrint
doesn't support -- the rule was silently dropped, leaving the card with no
background at all. Computed in Python instead (management/pdf.py) and baked
into the template as a plain hex value; the tint is based on the club's
primary_color, falling back to secondary_color when primary is itself (near)
black or white, where a straight tint would be invisible or too harsh.

Event forms: the location picker now shows "Name — City" (plus the country
when it isn't Belgium) and is searchable by name or city, reusing the
existing single-select searchable-select.js widget.

Games API: GameOut now carries `end` (explicit, or start + 2h when a GAME was
saved without one -- Event.save() sets this, never overwriting an explicit
end; other event kinds are untouched). /games/upcoming/ now includes
anything not yet finished rather than only things that haven't started, so a
game already in progress keeps showing up until its window closes; `status`
was adjusted to match so a game returned there never calls itself
"finished".

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

events/services/referees.py

@@ -21,22 +21,17 @@ only (still counts against Event.max_referees, still capacity-checked), for
 e.g. a federation-appointed referee the club still needs to pay.
 """
 
-import datetime
 from decimal import Decimal
 
 from django.db import transaction
 from django.utils import timezone
 from django.utils.translation import gettext_lazy as _
 
-from events.models import Event, EventReferee
+from events.models import ASSUMED_EVENT_DURATION, Event, EventReferee
 from events.services.attendance import effective_members
 from members.models import Member
 from teams.models import Team
 
-# Used only to give an event with no explicit `end` a time window for the
-# overlap check below -- never written back to the event itself.
-ASSUMED_EVENT_DURATION = datetime.timedelta(hours=2)
-
 
 class RefereeAssignmentError(Exception):
     """A referee could not be assigned to a game."""