Add Coach mode C4: create event, reusing the desktop's own EventForm

management.forms.EventForm already scopes its teams field to
teams_managed_by(user, club) via EventAudienceFormMixin -- exactly the
restriction a coach needs, so it's reused as-is rather than duplicated.
Only a subset of the desktop form's fields is rendered (title, kind, teams,
location, start, answers-close deadline); the rest stays unset, all of it
optional on the model except max_referees, which is dropped from the form
entirely so its own default (2) applies instead of demanding a value this
screen has no field for.

After a successful save, replicates management.views.EventCreateView's own
notify_new_event.delay(...) call by hand, since this isn't a CreateView --
attendance sync itself is automatic via events/signals.py.

"Repeat weekly" from the design mock isn't wired up this stage -- the
recurring-series machinery is a separate form with its own fields; adding
it is later work, not something to fake with an inert toggle.

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

static/css/app.css

@@ -3453,6 +3453,9 @@
   .-mt-4 {
     margin-top: calc(var(--spacing) * -4);
   }
+  .-mt-5 {
+    margin-top: calc(var(--spacing) * -5);
+  }
   .mt-0 {
     margin-top: 0;
   }
@@ -3917,6 +3920,9 @@
   .h-11 {
     height: calc(var(--spacing) * 11);
   }
+  .h-12 {
+    height: calc(var(--spacing) * 12);
+  }
   .h-14 {
     height: calc(var(--spacing) * 14);
   }
@@ -5528,6 +5534,11 @@
       outline-style: none;
     }
   }
+  .has-checked\:text-white {
+    &:has(*:checked) {
+      color: var(--color-white);
+    }
+  }
   .sm\:col-span-2 {
     @media (width >= 40rem) {
       grid-column: span 2 / span 2;