Notify members when a new event is planned

New events.tasks.notify_new_event, scheduled from
management.views.EventCreateView.form_valid -- the deliberate "a staff
member planned one new event" action, not every Event row that happens
to get created. A recurring series' rolling-horizon extension
(extend_event_series) and bulk fixture imports are NOT wired to this on
purpose: either would flood everyone with one push per occurrence
instead of the single, deliberate action this is meant to catch.

Notifies whoever is still NO_RESPONSE right after creation -- exactly
"everyone who needs to respond", using the existing notify_members() ->
Notification -> mobile.signals push chain already in place, so this is
in-app (visible in the M7 inbox, mark read/mark-all-read) and a push
notification both, with no new plumbing needed there.

Generalized mobile.views.NotificationsView's News-only "tap to open the
source" handling (previously isinstance(source, News)) into
_notification_source_link, covering Event sources too -- tapping an
"new event" notification now marks it read and opens the event's answer
screen, the same way a news notification already opened the article.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ECGMEwrc2k4D8VQuwjstj9

management/views.py

@@ -42,6 +42,7 @@ from events.services.competitions import CompetitionFetchError, fetch_game_info
 from events.services.rbihf_import import RBIHFImportError, apply_plan, build_plan, extract_team_id, fetch_html
 from events.services.recurrence import cancel_occurrence, detach_occurrence, generate_occurrences, propagate_series
 from events.services.referees import RefereeAssignmentError, add_external_referee, assign_referee, conflicting_events, eligible_referees, needs_referee_management, remove_referee, set_referee_fee
+from events.tasks import notify_new_event
 from formbuilder.models import Form as FormBuilderForm
 from formbuilder.models import Submission
 from members.forms import ClaimRejectForm, ClaimReviewForm
@@ -2795,6 +2796,10 @@ class EventCreateView(ClubStaffRequiredMixin, CreateView):
         response = super().form_valid(form)
         body = _("“%(event)s” created.") % {"event": self.object}
         notify(self.request, f"s|{_('Event created')}|{body}")
+        # A deliberately-planned single event, not every Event row that ends up
+        # created (see notify_new_event's own docstring for why a recurring
+        # series' occurrences and bulk fixture imports aren't wired to this).
+        notify_new_event.delay(str(self.object.pk))
         return response
 
     def get_success_url(self):