Feature: Multi-email alerts and move resource between groups

- notificationService.js: Parse comma-separated emails from resource.email_to or global config; validate and send to each recipient
- index.js: Add PATCH /api/resources/:id/group endpoint to move resource between groups with validation and cache invalidation
- App.js: Add group selector to edit modal; wire group change to PATCH endpoint; add help text for multi-email format (comma-separated)

server/notificationService.js

@@ -124,7 +124,7 @@ class NotificationService {
     return currentTime >= startTime && currentTime < endTime;
   }
 
-  async sendEmail(resource, message, type, stats = null) {
+  async sendEmail(resource, message, type, stats = null, emailOverride = null) {
     if (!this.transporter) {
       console.error(`[Email] Config incomplete; skipping email (enabled=${this.emailEnabled}, host=${this.config.email_host})`);
       return;