Add first-class hosting subdomain create/attach in Domains panel.

Customers can create label-based subdomains under primary/addon sites with a separate max_domains×5 quota, nginx/docroot/SSL provisioning, and managed DNS A records when Ladill controls the parent zone.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/Http/Controllers/Hosting/HostingProductController.php

@@ -209,7 +209,7 @@ class HostingProductController extends Controller
         $renewals ??= app(HostingRenewalCheckoutService::class);
 
         $account->load(['product', 'user', 'node', 'sites']);
-        $maxDomains = $account->resource_limits['max_domains'] ?? $account->product?->max_domains ?? 1;
+        $maxDomains = $account->maxDomainsLimit();
         $freeEmailAllowance = $account->freeEmailAllowance();
         $mailboxes = $account->loadedMailboxes();
         $mailboxCount = $mailboxes->count();
@@ -219,7 +219,7 @@ class HostingProductController extends Controller
             'account' => $account,
             'linkedSites' => $account->sites->sortBy(fn ($site) => [$site->type !== 'primary', $site->domain])->values(),
             'maxDomains' => $maxDomains,
-            'canLinkMoreDomains' => $account->sites->count() < $maxDomains,
+            'canLinkMoreDomains' => $account->canAddDomain(),
             'ownedDomains' => collect($this->getUserDomains($request->user())),
             'emailUsage' => [
                 'mailbox_count' => $mailboxCount,