Add server ownership, team access, role-based UI, and default admin role

- New migration 002_server_access.sql: created_by column + server_user table
- Server model: ownership, permission checks, team management methods
- Routes: /team routes, RoleMiddleware on /servers/create and /admin
- ServerController: permission checks via server_user, team CRUD methods
- TerminalController: server access checks
- DashboardController: filter servers by accessible ones
- ApiController: server access checks
- Views: team.php, team_server.php, sidebar Team link, hide actions by role
- Default user role changed from operator to admin on registration
- Admin user form defaults to admin role

src/Controllers/AdminController.php

@@ -62,7 +62,7 @@ class AdminController
             'username' => $_POST['username'],
             'email' => $_POST['email'],
             'password' => $_POST['password'],
-            'role' => $_POST['role'],
+            'role' => $_POST['role'] ?? 'admin',
             'is_active' => 1,
         ]);
 
@@ -159,6 +159,11 @@ class AdminController
 
     public function securitySettings(): void
     {
+        if (Session::get('user_role') !== 'super_admin') {
+            Session::setFlash('error', 'You do not have permission to access this page.');
+            $this->view->redirect('/dashboard');
+        }
+
         $this->view->display('admin.security', [
             'title' => 'Security Settings - ServerManager',
         ]);