Scaffold the mobile member app: PWA shell, push, and app-shell tokens

New `mobile` Django app mounted at /app/ -- the installed PWA for Member
mode (M1-M7, see design_handoff_rosterchief_platform/README.md). Coach
mode (C1-C6) is a later phase and has no routes yet.

Foundation pieces:
- assets/mobile.css: Tailwind v4 theme reusing management.css's design
  tokens (same per-club --tenant-* theming pattern), plus the ice/coach
  accent and mobile's 14px card radius.
- PushSubscription model + pywebpush-based sender (mobile/services/push.py),
  wired to notifications.Notification via a post_save signal so the
  existing notification system gains a push channel without knowing about
  PWAs itself.
- Per-club manifest.webmanifest + service worker (served at /app/sw.js)
  + a server-rendered fallback home-screen icon (club initials on
  secondary_color) for clubs without an uploaded logo -- confirmed with
  the user as the fallback, never a generic RosterChief mark.
- App shell (base.html): navy header, person switcher (every child a
  signed-in parent manages, plus "Me"), bottom tab bar, safe-area insets.
  Vendored htmx + Alpine for the screens built on top of it.
- Placeholder views/routes for all seven M1-M7 screens so the shell is
  fully wired end-to-end before each screen is built out individually.

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

mobile/migrations/0001_initial.py

@@ -0,0 +1,37 @@
+# Generated by Django 6.0.6 on 2026-08-21 08:23
+
+import django.db.models.deletion
+import uuid
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+        ('club', '0029_duesinvoice'),
+        ('members', '0006_parentclaim_submitted_by_user'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='PushSubscription',
+            fields=[
+                ('created', models.DateTimeField(auto_now_add=True, verbose_name='created')),
+                ('modified', models.DateTimeField(auto_now=True, verbose_name='modified')),
+                ('id', models.UUIDField(default=uuid.uuid4, editable=False, primary_key=True, serialize=False)),
+                ('endpoint', models.URLField(max_length=500, unique=True, verbose_name='endpoint')),
+                ('p256dh', models.CharField(max_length=255, verbose_name='p256dh key')),
+                ('auth', models.CharField(max_length=255, verbose_name='auth key')),
+                ('user_agent', models.CharField(blank=True, max_length=255, verbose_name='user agent')),
+                ('club', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='%(class)ss', to='club.club')),
+                ('member', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='push_subscriptions', to='members.member', verbose_name='member')),
+            ],
+            options={
+                'verbose_name': 'push subscription',
+                'verbose_name_plural': 'push subscriptions',
+                'ordering': ['-created'],
+            },
+        ),
+    ]