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/layouts/BusinessLayout.tsx

@@ -4,6 +4,7 @@ import Sidebar from '../components/Sidebar';
 import TopBar from '../components/TopBar';
 import TrialBanner from '../components/TrialBanner';
 import SandboxBanner from '../components/SandboxBanner';
+import QuotaWarningBanner from '../components/QuotaWarningBanner';
 import { Business, User } from '../types';
 import MasqueradeBanner from '../components/MasqueradeBanner';
 import OnboardingWizard from '../components/OnboardingWizard';
@@ -283,6 +284,10 @@ const BusinessLayoutContent: React.FC<BusinessLayoutProps> = ({ business, user,
             onStop={handleStopMasquerade}
           />
         )}
+        {/* Quota overage warning banner - show for owners and managers */}
+        {user.quota_overages && user.quota_overages.length > 0 && (
+          <QuotaWarningBanner overages={user.quota_overages} />
+        )}
         {/* Sandbox mode banner */}
         <SandboxBannerWrapper />
         {/* Show trial banner if trial is active and payments not yet enabled */}