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>

dashcaddy-api/routes/notifications.js

@@ -1,5 +1,6 @@
 const express = require('express');
 const { validateURL, validateToken } = require('../input-validator');
+const validatorLib = require('validator');
 const { paginate, parsePaginationParams } = require('../pagination');
 const { ValidationError } = require('../errors');
 
@@ -32,6 +33,12 @@ module.exports = function({ notification, asyncHandler }) {
             enabled: notificationConfig.providers.ntfy?.enabled || false,
             configured: !!notificationConfig.providers.ntfy?.topic,
             serverUrl: notificationConfig.providers.ntfy?.serverUrl || 'https://ntfy.sh'
+          },
+          email: {
+            enabled: notificationConfig.providers.email?.enabled || false,
+            configured: !!(notificationConfig.providers.email?.host && notificationConfig.providers.email?.to),
+            host: notificationConfig.providers.email?.host || '',
+            from: notificationConfig.providers.email?.from || ''
           }
         },
         events: notificationConfig.events,
@@ -74,6 +81,19 @@ module.exports = function({ notification, asyncHandler }) {
             throw new ValidationError('Invalid ntfy topic (alphanumeric, hyphens, underscores only, max 64 chars)');
           }
         }
+        if (providers.email?.to) {
+          const emails = providers.email.to.split(',').map(e => e.trim());
+          for (const email of emails) {
+            if (!validatorLib.isEmail(email)) {
+              throw new ValidationError(`Invalid email address: ${email}`);
+            }
+          }
+        }
+        if (providers.email?.host && typeof providers.email.host === 'string') {
+          if (!validatorLib.isFQDN(providers.email.host) && !validatorLib.isIP(providers.email.host)) {
+            throw new ValidationError('Invalid SMTP host');
+          }
+        }
       }
 
       // Update enabled state
@@ -101,6 +121,12 @@ module.exports = function({ notification, asyncHandler }) {
             ...providers.ntfy
           };
         }
+        if (providers.email) {
+          notificationConfig.providers.email = {
+            ...notificationConfig.providers.email,
+            ...providers.email
+          };
+        }
       }
 
       // Update events
@@ -144,6 +170,9 @@ module.exports = function({ notification, asyncHandler }) {
         case 'ntfy':
           result = await notification.sendNtfy('Test Notification', 'This is a test notification from DashCaddy.', 'info');
           break;
+        case 'email':
+          result = await notification.sendEmail('Test Notification', 'This is a test notification from DashCaddy.', 'info');
+          break;
         default:
           throw new ValidationError('Unknown provider');
       }