Preferences in Settings and a home page the user chooses

Settings gets a Preferences section: theme, default Bible, the Bible new reading
plans start in, verse layout, commentary, text size, reading width, audio
narrator (the last three stay per device; text size and narrator are now
remembered). A Home page setting (My Studies, Bible Reader or Reading Plans)
decides where the app opens and where every Home button goes; already being
there means My Studies. Back arrows are labelled Home. Tests cover every page
leading back.

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

src/components/reader/ReaderBars.jsx

@@ -9,7 +9,7 @@ export function TopBar({ title, onBack, onOpenNavigator, onSearch, onBookmarks,
   return (
     <div className="sticky top-0 z-30 border-b border-[var(--r-line)] bg-[var(--r-bar)] font-sans">
       <div className="mx-auto flex h-12 max-w-4xl items-center gap-1 px-2">
-        <button type="button" onClick={onBack} className={iconBtn} aria-label="Back to studies"><ChevronLeft /></button>
+        <button type="button" onClick={onBack} className="flex h-9 items-center gap-0.5 rounded-lg pl-1 pr-2 text-[var(--r-sub)] transition hover:bg-black/5" aria-label="Back to home"><ChevronLeft /><span className="hidden text-xs sm:inline">Home</span></button>
         <button type="button" onClick={onOpenNavigator}
           className="mx-auto flex min-w-0 items-center gap-1.5 rounded-lg px-3 py-1.5 text-sm font-medium text-[var(--r-text)] hover:bg-black/5">
           <span className="truncate">{title}</span><ChevronDown />