Stop the page extending under the status bar; use visible-viewport units

Drops viewport-fit=cover so the iPad/iPhone status bar is its own area and the system's
top-edge blur no longer covers the app bar. Fixed-height study stages are position:fixed so
they cannot scroll the document, and min-h-screen/100vh become dvh units.

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

src/components/study/PageShell.jsx

@@ -64,7 +64,7 @@ export default function PageShell({ title, onBack, actions, active = null, maxWi
   const { readerTheme, goHome, goStudies, openBibleReader, openReadingPlans } = useApp();
   const go = { studies: goStudies, reader: openBibleReader, plans: openReadingPlans };
   return (
-    <div className="min-h-screen bg-[var(--r-bg)] font-sans text-[var(--r-text)]" style={themeVars(readerTheme)}>
+    <div className="min-h-dvh bg-[var(--r-bg)] font-sans text-[var(--r-text)]" style={themeVars(readerTheme)}>
       <header className="safe-top sticky top-0 z-30 border-b border-[var(--r-line)] bg-[var(--r-bar)]">
         <div className={`mx-auto flex h-12 ${maxWidth} items-center gap-4 px-4`}>
           <button type="button" onClick={goHome} className="flex shrink-0 items-center gap-2" aria-label="Bible Study home">