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/mixins.py

@@ -0,0 +1,69 @@
+"""Shared scaffolding for every Member-mode screen (design_handoff_rosterchief_platform/
+README.md: "there is no parent app... every per-member screen carries a person
+switcher at the top" + "the [Coach/Member] switcher only renders for an account
+holding >=1 staff role"). One mixin so M1-M7's views (and the subagents building
+them) don't each re-derive this.
+"""
+
+from django.conf import settings
+
+from club.services.access import current_season, has_management_access
+from members.models import FamilyMembership, Member
+from members.views import ClubScopedPublicMixin
+from notifications.models import Notification
+
+
+class PersonScopeMixin(ClubScopedPublicMixin):
+    """Resolves the signed-in account's own Member record plus every child
+    they're a parent/guardian of *in this club* (mirrors members.views.MyFamilyView's
+    own query -- kept separate rather than imported from there, since that view
+    is public/unauthenticated-reachable and this one is always behind login).
+
+    ``?as=<member-id>`` re-scopes the current screen to one managed person,
+    same as the design doc's horizontally-scrolling chip row -- it re-scopes in
+    place rather than navigating. Falls back to the account's own Member, then
+    to the first managed child (e.g. a parent with no Member record of their own).
+    """
+
+    def dispatch(self, request, *args, **kwargs):
+        self.me = Member.objects.filter(user=request.user).first() if request.user.is_authenticated else None
+        self.managed_people = self._managed_people(request)
+        self.scope_person = self._resolve_scope_person(request)
+        return super().dispatch(request, *args, **kwargs)
+
+    def _managed_people(self, request):
+        if self.me is None:
+            return []
+        children = list(
+            Member.objects.filter(
+                family_memberships__role=FamilyMembership.FamilyRole.CHILD,
+                family_memberships__family__memberships__member=self.me,
+                family_memberships__family__memberships__role__in=[FamilyMembership.FamilyRole.PARENT, FamilyMembership.FamilyRole.GUARDIAN],
+                member_of__club=request.club,
+            ).distinct()
+        )
+        return [self.me, *children]
+
+    def _resolve_scope_person(self, request):
+        requested_id = request.GET.get("as")
+        if requested_id:
+            for person in self.managed_people:
+                if str(person.pk) == requested_id:
+                    return person
+        return self.managed_people[0] if self.managed_people else None
+
+    def get_context_data(self, **kwargs):
+        unread_notification_count = 0
+        if self.managed_people:
+            unread_notification_count = Notification.objects.filter(club=self.request.club, member__in=self.managed_people, read_at__isnull=True).count()
+
+        return super().get_context_data(
+            me=self.me,
+            managed_people=self.managed_people,
+            scope_person=self.scope_person,
+            has_staff_access=self.me is not None and has_management_access(self.request.user, self.request.club),
+            unread_notification_count=unread_notification_count,
+            season=current_season(self.request.club),
+            vapid_public_key=settings.VAPID_PUBLIC_KEY,
+            **kwargs,
+        )