Remove OnboardingRequirement.order; restrict checklist actions to admin/MEMBER_ADMIN

Every active requirement blocks equally and there's no set order to complete
them in, so the configurable "order" field (and its ordering-by-number) is
gone -- requirements list alphabetically now, both in the admin UI and the
Onboarding requirements settings page.

Also closes a real permission gap found while checking this: marking a
checklist item complete, bypassing it, or reopening it (management/views.py's
MemberRequirementCompleteView/BypassView/IncompleteView) was open to *any*
staff member with page access, not just admin/MEMBER_ADMIN, despite the
member detail page's own Documents card implying otherwise. Switched all
three to MemberAdminRequiredMixin and hid the corresponding buttons/dialog
from anyone who can't use them. The Sign-up page's Bypass action was already
admin-only end to end (the whole page is ClubAdminRequiredMixin-gated), so
no change in practice there.

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

club/migrations/0028_alter_onboardingrequirement_options_and_more.py

@@ -0,0 +1,21 @@
+# Generated by Django 6.0.6 on 2026-08-20 07:21
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('club', '0027_club_website'),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name='onboardingrequirement',
+            options={'ordering': ['name'], 'verbose_name': 'onboarding requirement', 'verbose_name_plural': 'onboarding requirements'},
+        ),
+        migrations.RemoveField(
+            model_name='onboardingrequirement',
+            name='order',
+        ),
+    ]