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/components/study/StudioShell.jsx

@@ -3,7 +3,7 @@
 // the stage switcher, and save/sync status.
 import { useApp } from '../../context/AppContext.js';
 import { themeVars, READER_THEMES } from '../reader/readerThemes.js';
-import { ChevronLeft } from '../reader/icons.jsx';
+import HomeButton from '../reader/HomeButton.jsx';
 
 export const STAGES = [
   { id: 'setup', label: 'Chunks' },
@@ -27,8 +27,7 @@ export default function StudioShell({ stage, loading = false, fixedHeight = fals
     <div className={`bg-[var(--r-bg)] font-sans text-[var(--r-text)] ${fixedHeight ? 'fixed inset-0 flex flex-col overflow-hidden' : 'min-h-dvh'}`} style={themeVars(readerTheme)}>
       <div className="safe-top z-30 shrink-0 border-b border-[var(--r-line)] bg-[var(--r-bar)]">
         <div className="mx-auto flex h-12 max-w-[1600px] items-center gap-3 px-3">
-          <button type="button" onClick={goHome} aria-label="Back to home"
-            className="flex h-9 items-center gap-0.5 rounded-lg pl-1 pr-2 text-[var(--r-sub)] hover:bg-black/5"><ChevronLeft /><span className="hidden text-xs sm:inline">Home</span></button>
+          <HomeButton onClick={goHome} />
           <div className="min-w-0 max-w-[16rem] truncate text-sm font-medium">{project?.title ?? ''}</div>
           <nav aria-label="Study stages" className="mx-auto flex gap-0.5">
             {STAGES.map((s) => {