fix: toolbar pushed off-screen on iPad Safari with tabs

On iPad Safari with the tab bar visible, `100vh` extends behind the
browser chrome, pushing the fixed-position toolbar out of view.

- Add `viewport-fit=cover` to viewport meta tag
- Use `100dvh` with `100vh` fallback for body/.app height
- Set `--app-height` CSS variable from `visualViewport.height` via JS
- Offset fixed toolbar on iOS Safari using the layout/visual viewport delta

src/web/public/index.html

@@ -2,7 +2,7 @@
 <html lang="en">
 <head>
   <meta charset="UTF-8">
-  <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no">
+  <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no, viewport-fit=cover">
   <meta name="description" content="Claude Code session manager with web interface">
   <meta name="theme-color" content="#0a0a0a">
   <meta name="google" content="notranslate">
@@ -25,7 +25,7 @@
   <script>if(window.innerWidth<768||(('ontouchstart' in window||navigator.maxTouchPoints>0)&&window.innerWidth<1024))document.documentElement.classList.add('mobile-init');</script>
   <!-- Inline critical CSS for instant skeleton paint (before styles.css loads) -->
   <style>
-    .loading-skeleton{display:flex;flex-direction:column;height:100vh;background:#0a0a0a}
+    .loading-skeleton{display:flex;flex-direction:column;height:100vh;height:100dvh;background:#0a0a0a}
     .skeleton-header{height:40px;background:#111;border-bottom:1px solid #1a1a2e;display:flex;align-items:center;padding:0 12px}
     .skeleton-brand{color:#60a5fa;font-size:14px;font-weight:600;font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',sans-serif;opacity:.7}
     .skeleton-tabs{display:flex;gap:4px;margin-left:16px}