feat: Quota enforcement UI and various improvements

- Add quota limit warnings to Resources, Services, and OwnerScheduler pages
- Add quotaUtils.ts for checking quota limits
- Update BusinessLayout with quota context
- Improve email receiver logging
- Update serializers

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

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

frontend/src/layouts/BusinessLayout.tsx

@@ -5,6 +5,7 @@ import TopBar from '../components/TopBar';
 import TrialBanner from '../components/TrialBanner';
 import SandboxBanner from '../components/SandboxBanner';
 import QuotaWarningBanner from '../components/QuotaWarningBanner';
+import QuotaOverageModal, { resetQuotaOverageModalDismissal } from '../components/QuotaOverageModal';
 import { Business, User } from '../types';
 import MasqueradeBanner from '../components/MasqueradeBanner';
 import OnboardingWizard from '../components/OnboardingWizard';
@@ -108,9 +109,21 @@ const BusinessLayoutContent: React.FC<BusinessLayoutProps> = ({ business, user,
   }, []);
 
   const handleStopMasquerade = () => {
+    // Reset quota modal dismissal when returning from masquerade
+    resetQuotaOverageModalDismissal();
     stopMasqueradeMutation.mutate();
   };
 
+  // Reset quota modal when user changes (masquerade start)
+  const prevUserIdRef = useRef<string | undefined>(undefined);
+  useEffect(() => {
+    if (prevUserIdRef.current !== undefined && prevUserIdRef.current !== user.id) {
+      // User changed (masquerade started or changed) - reset modal
+      resetQuotaOverageModalDismissal();
+    }
+    prevUserIdRef.current = user.id;
+  }, [user.id]);
+
   useNotificationWebSocket(); // Activate the notification WebSocket listener
 
   // Get the previous user from the stack (the one we'll return to)
@@ -193,6 +206,10 @@ const BusinessLayoutContent: React.FC<BusinessLayoutProps> = ({ business, user,
         {user.quota_overages && user.quota_overages.length > 0 && (
           <QuotaWarningBanner overages={user.quota_overages} />
         )}
+        {/* Quota overage modal - shows once per session on login/masquerade */}
+        {user.quota_overages && user.quota_overages.length > 0 && (
+          <QuotaOverageModal overages={user.quota_overages} onDismiss={() => {}} />
+        )}
         {/* Sandbox mode banner */}
         <SandboxBannerWrapper />
         {/* Show trial banner if trial is active and payments not yet enabled */}