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/Services/Agent/AgentSiteProvisioningService.php

@@ -16,10 +16,33 @@ final class AgentSiteProvisioningService
         private readonly AgentProfileService $agentProfileService,
     ) {}
 
+    /**
+     * Generate a unique agent code based on site code and counter.
+     * Format: {site_code}-agent-{counter}
+     */
+    private function generateUniqueAgentCode(int $siteId): string
+    {
+        $site = AdminSite::query()->find($siteId);
+        if ($site === null) {
+            throw new \RuntimeException('Site not found');
+        }
+
+        $prefix = strtolower(trim($site->code));
+        $counter = 1;
+
+        while (true) {
+            $code = sprintf('%s-agent-%d', $prefix, $counter);
+            if (!AgentNode::query()->where('code', $code)->exists()) {
+                return $code;
+            }
+            $counter++;
+        }
+    }
+
     /**
      * 在已存在的接入站点上创建一级代理（根节点）及后台登录账号。
      *
-     * @param  array<string, mixed>  $payload  site_code, code, name, username, password, email?, status?, profile fields
+     * @param  array<string, mixed>  $payload  site_code, code?, name, username, password, email?, status?, profile fields
      * @return array{site: AdminSite, agent_node: AgentNode}
      */
     public function createRootAgent(AdminUser $actor, array $payload): array
@@ -32,10 +55,9 @@ final class AgentSiteProvisioningService
         $email = isset($payload['email']) ? trim((string) $payload['email']) : null;
         $status = (int) ($payload['status'] ?? 1);
 
-        if ($siteCode === '' || $code === '' || $name === '' || $username === '' || $password === '') {
+        if ($siteCode === '' || $name === '' || $username === '' || $password === '') {
             throw ValidationException::withMessages([
                 'site_code' => $siteCode === '' ? ['required'] : [],
-                'code' => $code === '' ? ['required'] : [],
                 'name' => $name === '' ? ['required'] : [],
                 'username' => $username === '' ? ['required'] : [],
                 'password' => $password === '' ? ['required'] : [],
@@ -47,8 +69,13 @@ final class AgentSiteProvisioningService
             throw ValidationException::withMessages(['site_code' => ['exists']]);
         }
 
-        if (AgentNode::query()->where('code', $code)->exists()) {
-            throw ValidationException::withMessages(['code' => ['unique']]);
+        // Auto-generate code if not provided
+        if ($code === '') {
+            $code = $this->generateUniqueAgentCode($site->id);
+        } else {
+            if (AgentNode::query()->where('code', $code)->exists()) {
+                throw ValidationException::withMessages(['code' => ['unique']]);
+            }
         }
 
         if (AdminUser::query()->where('username', $username)->exists()) {