Easier navigation on iPhone

- Phones get a bottom tab bar (Studies, Bible, Plans, Prayer, Account); wider screens keep the header nav
- The Account menu opens upward from the bar; toasts sit above it
- Reader and study pages get a labelled Home button instead of a small arrow

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/pages/AdminPage.jsx

@@ -70,7 +70,7 @@ export default function AdminPage() {
   };
 
   return (
-    <PageShell title="Admin" onBack={goHome} maxWidth="max-w-5xl">
+    <PageShell title="Admin" active="admin" onBack={goHome} maxWidth="max-w-5xl">
       <main className="mx-auto max-w-5xl space-y-5 px-4 py-6">
         <div className="flex gap-2">
           <button type="button" onClick={() => setAdminTab('users')}

src/pages/SettingsPage.jsx

@@ -235,7 +235,7 @@ export default function SettingsPage() {
   };
 
   return (
-    <PageShell title="Account Settings" onBack={goHome} maxWidth="max-w-2xl">
+    <PageShell title="Account Settings" active="settings" onBack={goHome} maxWidth="max-w-2xl">
       <main className="mx-auto max-w-2xl space-y-5 px-4 py-6">
         <div role="tablist" aria-label="Settings sections" className="-mx-1 flex gap-1 overflow-x-auto px-1 pb-1">
           {SETTINGS_TABS.map(([id, label]) => (