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/reader/icons.jsx

@@ -2,6 +2,7 @@
 const base = { viewBox: '0 0 20 20', width: 20, height: 20, fill: 'none', stroke: 'currentColor', strokeWidth: 1.6, strokeLinecap: 'round', strokeLinejoin: 'round', 'aria-hidden': true };
 
 export const ChevronLeft = () => <svg {...base}><path d="M12 4l-6 6 6 6" /></svg>;
+export const HomeIcon = () => <svg {...base}><path d="M3.5 9.5L10 4l6.5 5.5M5 8.5V16h3.5v-4h3v4H15V8.5" /></svg>;
 export const ChevronRight = () => <svg {...base}><path d="M8 4l6 6-6 6" /></svg>;
 export const ChevronDown = ({ size = 14 }) => <svg {...base} width={size} height={size}><path d="M5 8l5 5 5-5" /></svg>;
 export const SearchIcon = () => <svg {...base}><circle cx="9" cy="9" r="5.5" /><path d="M13.5 13.5L17 17" /></svg>;