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

static/css/app.css

@@ -2774,6 +2774,9 @@
   .right-0 {
     right: 0;
   }
+  .right-1\.5 {
+    right: calc(var(--spacing) * 1.5);
+  }
   .right-2 {
     right: calc(var(--spacing) * 2);
   }
@@ -3853,6 +3856,9 @@
   .h-1\.5 {
     height: calc(var(--spacing) * 1.5);
   }
+  .h-2 {
+    height: calc(var(--spacing) * 2);
+  }
   .h-4 {
     height: calc(var(--spacing) * 4);
   }
@@ -3967,6 +3973,9 @@
   .w-1\.5 {
     width: calc(var(--spacing) * 1.5);
   }
+  .w-2 {
+    width: calc(var(--spacing) * 2);
+  }
   .w-4 {
     width: calc(var(--spacing) * 4);
   }
@@ -4741,6 +4750,9 @@
   .pt-4 {
     padding-top: calc(var(--spacing) * 4);
   }
+  .pb-0\.5 {
+    padding-bottom: calc(var(--spacing) * 0.5);
+  }
   .pb-2 {
     padding-bottom: calc(var(--spacing) * 2);
   }
@@ -4858,6 +4870,9 @@
   .text-\[17px\] {
     font-size: 17px;
   }
+  .text-\[19px\] {
+    font-size: 19px;
+  }
   .text-\[22px\] {
     font-size: 22px;
   }
@@ -5260,6 +5275,13 @@
       --btn-soft-bg: initial;
     }
   }
+  .btn-secondary {
+    @layer daisyui.l1.l2 {
+      --btn-color: var(--color-secondary);
+      --btn-fg: var(--color-secondary-content);
+      --btn-soft-bg: initial;
+    }
+  }
   .btn-sm {
     @layer daisyui.l1.l2 {
       --fontsize: 0.75rem;