fix(17-03): lift FAB above BottomTabBar and reserve phone content padding

- CalendarShell.tsx: FAB bottom changed from var(--space-6) to
  calc(var(--bottom-chrome-h) + var(--space-6)) — sits 24px above bar
- App.tsx: contentStyle gains phone-only paddingBottom: var(--bottom-chrome-h)
  via spread pattern ...(phone ? {...} : {}) — desktop unchanged

apps/pwa/src/App.tsx

@@ -160,6 +160,8 @@ export default function App() {
     flexDirection: 'column',
     overflow: 'hidden',
     position: 'relative',
+    // Phone-only: reserve space for the fixed BottomTabBar so content is not occluded
+    ...(phone ? { paddingBottom: 'var(--bottom-chrome-h)' } : {}),
   };
 
   // Setup gate: while setup status is loading, render nothing (prevent flash).