feat: Quota overage system, updated tier pricing, and communication addons

Quota Overage System:
- Add QuotaOverage model for tracking resource/user quota overages
- Implement 30-day grace period with email notifications (immediate, 7-day, 1-day)
- Add QuotaWarningBanner component in BusinessLayout
- Add QuotaSettings page for managing overages and archiving resources
- Add Celery tasks for automated quota checks and expiration handling
- Add quota management API endpoints

Updated Tier Pricing (Stripe: 2.9% + $0.30):
- Free: No payments (requires addon)
- Starter: 4% + $0.40
- Professional: 3.5% + $0.35
- Business: 3.25% + $0.32
- Enterprise: 3% + $0.30

New Subscription Addons:
- Online Payments ($5/mo + 5% + $0.50) - for Free tier
- SMS Notifications ($10/mo) - enables SMS reminders
- Masked Calling ($15/mo) - enables anonymous calling

BusinessEditModal Improvements:
- Increased width to match PlanModal (max-w-3xl)
- Added all tier options with auto-update on tier change
- Added limits configuration and permissions sections

Backend Fixes:
- Fixed SubscriptionPlan serializer to include all communication fields
- Allow blank business_tier for addon plans
- Added migration for business_tier field changes

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

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

frontend/src/App.tsx

@@ -84,6 +84,7 @@ const AuthenticationSettings = React.lazy(() => import('./pages/settings/Authent
 const EmailSettings = React.lazy(() => import('./pages/settings/EmailSettings'));
 const CommunicationSettings = React.lazy(() => import('./pages/settings/CommunicationSettings'));
 const BillingSettings = React.lazy(() => import('./pages/settings/BillingSettings'));
+const QuotaSettings = React.lazy(() => import('./pages/settings/QuotaSettings'));
 
 import { Toaster } from 'react-hot-toast'; // Import Toaster for notifications
 
@@ -705,6 +706,7 @@ const AppContent: React.FC = () => {
                 <Route path="email" element={<EmailSettings />} />
                 <Route path="sms-calling" element={<CommunicationSettings />} />
                 <Route path="billing" element={<BillingSettings />} />
+                <Route path="quota" element={<QuotaSettings />} />
               </Route>
             ) : (
               <Route path="/settings/*" element={<Navigate to="/" />} />