fix: correct subscription description when data unavailable (refs #55)

Fixed conditional logic for subscription description text to properly
handle the case when subscription data is not loaded or unavailable.

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/pages/SettingsPage.tsx

@@ -435,9 +435,9 @@ export const SettingsPage: React.FC = () => {
                 )}
               </Box>
               <Typography variant="body2" color="text.secondary">
-                {subscription?.tier === 'free'
+                {!subscription || subscription.tier === 'free'
                   ? 'Upgrade to Pro or Enterprise for more features and vehicle slots.'
-                  : subscription?.tier === 'pro'
+                  : subscription.tier === 'pro'
                   ? 'Pro plan with up to 5 vehicles and full features.'
                   : 'Enterprise plan with unlimited vehicles and all features.'}
               </Typography>