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/dashboard/index.php

@@ -65,7 +65,9 @@ $recentActivity = $recentActivity ?? [];
                 <div class="empty-state">
                     <i class="fas fa-server"></i>
                     <p>No servers configured yet.</p>
+                    <?php if (is_admin()): ?>
                     <a href="/servers/create" class="btn btn-primary">Add Server</a>
+                    <?php endif; ?>
                 </div>
             <?php else: ?>
                 <div class="table-responsive">