Add Coach mode C5: post news, reusing the desktop's own NewsForm

management.forms.NewsForm defaults its teams field to every club team --
fine for an editor/admin, but a real gap for a coach, who should only ever
post as their own team, never "on behalf of" one they don't run. Re-scoped
to teams_managed_by via self.managed_teams, and made required (a coach's
post is always team-scoped, never empty/club-wide -- that stays an
editor/admin claim).

Gated with club.services.access.can_add_news, which already includes
is_coach_manager. On submit the post goes straight to
News.submit_for_review() plus the same notify_editors_of_pending_review
call the desktop's own NewsSubmitForReviewView makes, landing in an
editor's queue instead of a silent draft. The button reads "Send" rather
than the mock's "Publish" -- can_publish_news stays editor/admin-only, so
that's the honest description of what actually happens.

visibility is left at the model's own INTERNAL default rather than
building the mock's "also on club website" toggle -- an editor reviewing
the pending post can widen it before publishing if a public-site
placement is actually warranted; that's a real gate, not a decorative
row, so it isn't reproduced as one here.

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

mobile/urls.py

@@ -26,4 +26,5 @@ urlpatterns = [
     path("coach/", coach_views.CoachTodayView.as_view(), name="coach_today"),
     path("coach/attendance/<uuid:event_id>/", coach_views.CoachAttendanceView.as_view(), name="coach_attendance"),
     path("coach/events/new/", coach_views.CoachCreateEventView.as_view(), name="coach_create_event"),
+    path("coach/news/new/", coach_views.CoachCreateNewsView.as_view(), name="coach_create_news"),
 ]