feat: Redesign mobile UI with centered voice button and user menu

- Repositioned Voice Command button to center of bottom navigation bar
- Added floating user menu icon in top-left corner on mobile
- User menu includes: Settings, Children, Family, and Logout options
- Updated bottom nav to show: Home, Track, Voice (center), Insights, History
- Hide original floating voice button on mobile to avoid duplication
- Improved mobile UX with easier thumb access to voice commands
- User avatar displays first letter of user's name

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

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

maternal-web/components/voice/VoiceFloatingButton.tsx

@@ -323,7 +323,7 @@ export function VoiceFloatingButton() {
 
   return (
     <>
-      {/* Floating button positioned in bottom-right */}
+      {/* Floating button positioned in bottom-right - Hidden on mobile since we have TabBar center button */}
       <Tooltip title="Voice Command (Beta)" placement="left">
         <Fab
           color="primary"
@@ -335,6 +335,7 @@ export function VoiceFloatingButton() {
             bottom: 24,
             right: 24,
             zIndex: 1000,
+            display: { xs: 'none', md: 'flex' }, // Hide on mobile (xs) and small screens, show on medium+
           }}
         >
           <MicIcon />