feat: add 7 new features — exec shell, SSE events, compose import, docker resources, resource limits, email notifications, auto-updates

- Container exec/shell via WebSocket + xterm.js (subtle >_ button on cards)
- Live dashboard updates via SSE (resource alerts, health changes, update notices)
- Docker Compose import with YAML parsing, preview, and dependency-ordered deploy
- Volume & network management modal with disk usage overview
- CPU/memory resource limits on deploy and live update
- Email SMTP notifications (nodemailer) alongside Discord/Telegram/ntfy
- Scheduled auto-update scheduler with maintenance windows (daily/weekly/monthly)

New deps: ws, js-yaml, nodemailer

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

status/js/core/grid.js

@@ -211,6 +211,15 @@
           window.updateContainer(s.containerId, s.name, s.id);
         };
         btnRow.appendChild(updateBtn);
+
+        // Terminal exec button (subtle — visible on hover)
+        const execBtn = el('button', 'exec-btn', '>_');
+        execBtn.title = 'Open terminal';
+        execBtn.onclick = (e) => {
+          e.stopPropagation();
+          if (window.openExecModal) window.openExecModal(s.containerId, s.name);
+        };
+        btnRow.appendChild(execBtn);
       }
 
       // Add logs button for services with logPath (native apps)