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

views/layouts/main.php

@@ -39,6 +39,12 @@
                             <div class="nav-submenu-loading"><i class="fas fa-spinner fa-spin"></i></div>
                         </div>
                     </li>
+                    <li class="nav-item">
+                        <a href="/team" class="nav-link <?= str_starts_with($_SERVER['REQUEST_URI'] ?? '', '/team') ? 'active' : '' ?>">
+                            <i class="fas fa-users-cog"></i>
+                            <span>Team</span>
+                        </a>
+                    </li>
                     <li class="nav-divider"></li>
                     <li class="nav-section">Administration</li>
                     <?php if (in_array($_SESSION['user_role'] ?? '', ['super_admin', 'admin'])): ?>