fix: Comprehensive authentication and UI fixes

Authentication & Token Management:
- Add deviceId to token refresh flow (backend requires both refreshToken and deviceId)
- Fix React Strict Mode token clearing race condition with retry logic
- Improve AuthContext to handle all token state combinations properly
- Store deviceId in localStorage alongside tokens

UI/UX Improvements:
- Remove deprecated legacyBehavior from Next.js Link components
- Update primary theme color to WCAG AA compliant #7c3aed
- Fix nested button error in TabBar voice navigation
- Fix invalid Tabs value error in DynamicChildDashboard

Multi-Child Dashboard:
- Load all children into Redux store properly
- Fetch metrics for all children, not just selected one
- Remove mock data to prevent unauthorized API calls

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

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

maternal-web/app/(auth)/register/page.tsx

@@ -484,11 +484,9 @@ export default function RegisterPage() {
           <Box sx={{ mt: 3, textAlign: 'center' }}>
             <Typography variant="body2" color="text.secondary">
               Already have an account?{' '}
-              <Link href="/login" passHref legacyBehavior>
-                <MuiLink sx={{ cursor: 'pointer', fontWeight: 600 }}>
-                  Sign in
-                </MuiLink>
-              </Link>
+              <MuiLink component={Link} href="/login" sx={{ cursor: 'pointer', fontWeight: 600 }}>
+                Sign in
+              </MuiLink>
             </Typography>
           </Box>
         </Paper>