Integrate VoiceFAB into tabs layout

Add floating action button for voice calls to the tab bar layout:
- Import and render VoiceFAB component
- Add placeholder handler for voice call initiation
- Wrap Tabs in View to properly position FAB overlay
- FAB automatically hides when a call is active (via VoiceCallContext)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/(tabs)/_layout.tsx

@@ -1,17 +1,32 @@
 import { Tabs } from 'expo-router';
-import React from 'react';
-import { Platform } from 'react-native';
+import React, { useCallback } from 'react';
+import { Platform, View, Alert } from 'react-native';
 import { Feather } from '@expo/vector-icons';
 import { useSafeAreaInsets } from 'react-native-safe-area-context';
 
 import { HapticTab } from '@/components/haptic-tab';
+import { VoiceFAB } from '@/components/VoiceFAB';
 import { AppColors } from '@/constants/theme';
 import { useColorScheme } from '@/hooks/use-color-scheme';
+import { useVoiceCall } from '@/contexts/VoiceCallContext';
 
 export default function TabLayout() {
   const colorScheme = useColorScheme();
   const isDark = colorScheme === 'dark';
   const insets = useSafeAreaInsets();
+  // VoiceFAB uses VoiceCallContext internally to hide when call is active
+  useVoiceCall(); // Ensure context is available
+
+  // Handle voice FAB press - initiate voice call
+  const handleVoiceFABPress = useCallback(() => {
+    // TODO: Integrate with LiveKit voice call when ready
+    // For now, show placeholder alert
+    Alert.alert(
+      'Voice Call',
+      'Voice call with Julia AI will be available soon.',
+      [{ text: 'OK' }]
+    );
+  }, []);
 
   // Calculate tab bar height based on safe area
   // On iOS with home indicator, insets.bottom is ~34px
@@ -24,6 +39,7 @@ export default function TabLayout() {
   const tabBarHeight = 60 + bottomPadding; // 60px for content + safe area padding
 
   return (
+    <View style={{ flex: 1 }}>
       <Tabs
         screenOptions={{
           tabBarActiveTintColor: AppColors.primary,
@@ -100,5 +116,9 @@ export default function TabLayout() {
           }}
         />
       </Tabs>
+
+      {/* Voice FAB - shown when no call is active */}
+      <VoiceFAB onPress={handleVoiceFABPress} />
+    </View>
   );
 }