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/AuthController.php

@@ -126,13 +126,13 @@ class AuthController
             'username' => $username,
             'email' => $email,
             'password' => $_POST['password'],
-            'role' => 'operator',
+            'role' => 'admin',
             'is_active' => 1,
         ]);
 
         $this->auditService->log('user_registered', 'user', $id, [
             'username' => $username,
-            'role' => 'operator',
+            'role' => 'admin',
         ]);
 
         Session::setFlash('success', 'Account created. You can now log in.');