Refactor registration and dashboard features to support invite codes and Bunny uploads

- Moved registration logic to a new client component for better separation of concerns.
- Integrated invite code requirement based on feature flags in the registration process.
- Enhanced dashboard functionality to conditionally enable Bunny uploads based on feature flags.
- Updated various components and API routes to check for Bunny uploads and Stripe billing feature flags.
- Added new feature flag utilities for managing feature toggles in the application.

app/api/billing/checkout/route.ts

@@ -7,6 +7,7 @@ import {
   getStripeCheckoutState,
 } from '@/lib/billing';
 import { rateLimit } from '@/lib/rate-limit';
+import { isStripeFeatureEnabled } from '@/lib/feature-flags';
 import { getStripe, getStripePriceId, isStripeConfigured } from '@/lib/stripe';
 import { isTrustedSameOriginRequest } from '@/lib/request-origin';
 
@@ -35,6 +36,10 @@ export async function POST(request: NextRequest) {
       return apiErrors.unauthorized();
     }
 
+    if (!isStripeFeatureEnabled()) {
+      return apiErrors.badRequest('Stripe billing is disabled by this host');
+    }
+
     if (!isStripeConfigured()) {
       return apiErrors.internalError('Stripe billing is not configured');
     }