feat: refactor super admin to use is_super_admin flag and enhance site deletion logic

- Changed super admin detection from role-based to `is_super_admin` flag in AdminUser model
- Added `requireDefaultAdminSiteId()` method to throw validation error when no integration site exists
- Enhanced site deletion to migrate platform role bindings to fallback site and auto-delete site-specific admin accounts
- Made agent line code optional with auto-generation fallback using `{site_code}-agent-{counter}` format

app/Support/AdminAuthProfile.php

@@ -38,6 +38,7 @@ final class AdminAuthProfile
      *     can_create_child_agent: bool,
      *     can_create_player: bool
      *   },
+     *   site: ?array{id: int, code: string, name: string},
      *   is_super_admin: bool,
      *   operational_permissions: list<string>,
      *   delegation_ceiling: list<string>,
@@ -58,6 +59,7 @@ final class AdminAuthProfile
             'permissions' => $permissionSlugs,
             'navigation' => AdminAuthorizationRegistry::visibleNavigationItems($permissionSlugs, $fresh),
             'agent' => $agent,
+            'site' => self::siteContext($fresh),
             'is_super_admin' => $fresh->isSuperAdmin(),
             'operational_permissions' => $permissionSlugs,
             'delegation_ceiling' => AgentDelegationAuthorization::delegationLegacySlugsForAdminUser($fresh),
@@ -71,19 +73,32 @@ final class AdminAuthProfile
     }
 
     /**
-     * @return array{
-     *   id: int,
-     *   admin_site_id: int,
-     *   admin_site_name: string,
-     *   site_code: string,
-     *   path: string,
-     *   code: string,
-     *   name: string,
-     *   depth: int,
-     *   can_create_child_agent: bool,
-     *   can_create_player: bool
-     * }|null
+     * @return array{id: int, code: string, name: string}|null
      */
+    private static function siteContext(AdminUser $admin): ?array
+    {
+        if ($admin->isSuperAdmin() || $admin->primaryAgentNode() !== null) {
+            return null;
+        }
+
+        if (! SitePlatformRole::userHasSiteAdminRole($admin)) {
+            return null;
+        }
+
+        $sites = AdminUserSiteBindingPresenter::accessibleSitesFor($admin);
+        if ($sites === []) {
+            return null;
+        }
+
+        $site = $sites[0];
+
+        return [
+            'id' => (int) $site['id'],
+            'code' => (string) $site['code'],
+            'name' => (string) $site['name'],
+        ];
+    }
+
     private static function agentContext(AdminUser $admin): ?array
     {
         if ($admin->isSuperAdmin()) {