feat: implement upgrade to premium flow

This commit adds the ability for tenants to upgrade their package directly from the mobile billing page. It includes:
- New API function createTenantPaddleCheckout in api.ts
- Upgrade handler and UI in BillingPage.tsx
- Updated navigation in EventAnalyticsPage.tsx to link to the packages section of the billing page

resources/js/admin/api.ts

@@ -2454,6 +2454,25 @@ export async function getTenantPaddleTransactions(cursor?: string): Promise<{
   };
 }
 
+export async function createTenantPaddleCheckout(
+  packageId: number,
+  urls?: { success_url?: string; return_url?: string }
+): Promise<{ checkout_url: string; id: string; expires_at?: string }> {
+  const response = await authorizedFetch('/api/v1/tenant/packages/paddle-checkout', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({
+      package_id: packageId,
+      success_url: urls?.success_url,
+      return_url: urls?.return_url,
+    }),
+  });
+  return await jsonOrThrow<{ checkout_url: string; id: string; expires_at?: string }>(
+    response,
+    'Failed to create checkout'
+  );
+}
+
 export async function createTenantBillingPortalSession(): Promise<{ url: string }> {
   const response = await authorizedFetch('/api/v1/tenant/billing/portal', {
     method: 'POST',