feat: add Settings (user management) and Notifications pages

Backend:
- User management API: GET/POST/PUT/DELETE /api/users
  Supports two roles: developer, server-admin
  Each user has notifyOnError toggle for email alerts
- Notification API: GET /api/notifications, mark read, unread count
- Email service: sends alerts via SMTP (mail.bshtech.net/noreply@bshtech.net)
  to all users with notifyOnError=true on error/warning events
- Health monitor: checks CPU, memory, disk, Docker containers every 60s
  Creates notifications + sends email on threshold breaches
  Detects container down, high CPU (>90%), memory (>90%), disk (>85%)
  Sends recovery notifications when issues resolve
- File-based JSON storage for users and notifications (data/ directory)
- Added nodemailer dependency

Frontend:
- Settings page: user list with role badges, email alert toggles,
  add/remove user forms. Roles: Developer (blue), Server Admin (amber)
- Notifications page: real-time alert feed with type icons (error/warning/
  info/recovery), read/unread state, email sent indicator, time ago display
- Added Notifications to sidebar navigation
- Wired both pages into App.tsx router

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/services/notifications.ts

@@ -0,0 +1,192 @@
+// server/src/services/notifications.ts
+import { createTransport } from 'nodemailer';
+import { readFileSync, writeFileSync, existsSync } from 'fs';
+import { resolve } from 'path';
+import { randomUUID } from 'crypto';
+import type { MonitorUser, Notification, UserRole } from '../types/index.js';
+
+// ─── Persistent JSON storage (simple file-based) ───
+const DATA_DIR = resolve(process.cwd(), 'data');
+const USERS_FILE = resolve(DATA_DIR, 'users.json');
+const NOTIFICATIONS_FILE = resolve(DATA_DIR, 'notifications.json');
+
+function ensureDataDir() {
+  const { mkdirSync } = require('fs');
+  try { mkdirSync(DATA_DIR, { recursive: true }); } catch {}
+}
+
+function loadUsers(): MonitorUser[] {
+  ensureDataDir();
+  if (!existsSync(USERS_FILE)) {
+    // Seed with the existing config users
+    const seed: MonitorUser[] = [
+      { id: randomUUID(), email: 'nafih@bshtechnologies.in', name: 'Nafih', role: 'server-admin', notifyOnError: true, createdAt: new Date().toISOString() },
+      { id: randomUUID(), email: 'vivek@bshtechnologies.in', name: 'Vivek', role: 'developer', notifyOnError: true, createdAt: new Date().toISOString() },
+    ];
+    writeFileSync(USERS_FILE, JSON.stringify(seed, null, 2));
+    return seed;
+  }
+  return JSON.parse(readFileSync(USERS_FILE, 'utf-8'));
+}
+
+function saveUsers(users: MonitorUser[]) {
+  ensureDataDir();
+  writeFileSync(USERS_FILE, JSON.stringify(users, null, 2));
+}
+
+function loadNotifications(): Notification[] {
+  ensureDataDir();
+  if (!existsSync(NOTIFICATIONS_FILE)) {
+    writeFileSync(NOTIFICATIONS_FILE, '[]');
+    return [];
+  }
+  return JSON.parse(readFileSync(NOTIFICATIONS_FILE, 'utf-8'));
+}
+
+function saveNotifications(notifs: Notification[]) {
+  ensureDataDir();
+  // Keep only last 200 notifications
+  const trimmed = notifs.slice(-200);
+  writeFileSync(NOTIFICATIONS_FILE, JSON.stringify(trimmed, null, 2));
+}
+
+// ─── SMTP Transport ───
+const smtpTransport = createTransport({
+  host: process.env.SMTP_HOST ?? 'mail.bshtech.net',
+  port: parseInt(process.env.SMTP_PORT ?? '587'),
+  secure: false,
+  auth: {
+    user: process.env.SMTP_USER ?? 'noreply@bshtech.net',
+    pass: process.env.SMTP_PASS ?? 'Ev3ntifyN0Reply2026',
+  },
+  tls: { rejectUnauthorized: false },
+});
+
+// ─── Public API ───
+
+export function getUsers(): MonitorUser[] {
+  return loadUsers();
+}
+
+export function addUser(email: string, name: string, role: UserRole, notifyOnError = true): MonitorUser {
+  const users = loadUsers();
+  if (users.find(u => u.email === email)) {
+    throw new Error(`User with email ${email} already exists`);
+  }
+  const user: MonitorUser = {
+    id: randomUUID(),
+    email,
+    name,
+    role,
+    notifyOnError,
+    createdAt: new Date().toISOString(),
+  };
+  users.push(user);
+  saveUsers(users);
+  return user;
+}
+
+export function updateUser(id: string, updates: Partial<Pick<MonitorUser, 'name' | 'role' | 'notifyOnError'>>): MonitorUser {
+  const users = loadUsers();
+  const idx = users.findIndex(u => u.id === id);
+  if (idx < 0) throw new Error('User not found');
+  users[idx] = { ...users[idx], ...updates };
+  saveUsers(users);
+  return users[idx];
+}
+
+export function deleteUser(id: string): void {
+  const users = loadUsers();
+  const filtered = users.filter(u => u.id !== id);
+  if (filtered.length === users.length) throw new Error('User not found');
+  saveUsers(filtered);
+}
+
+export function getNotifications(limit = 50): Notification[] {
+  return loadNotifications().reverse().slice(0, limit);
+}
+
+export function markNotificationRead(id: string): void {
+  const notifs = loadNotifications();
+  const n = notifs.find(n => n.id === id);
+  if (n) {
+    n.read = true;
+    saveNotifications(notifs);
+  }
+}
+
+export function markAllRead(): void {
+  const notifs = loadNotifications();
+  notifs.forEach(n => n.read = true);
+  saveNotifications(notifs);
+}
+
+export function getUnreadCount(): number {
+  return loadNotifications().filter(n => !n.read).length;
+}
+
+export async function createNotification(
+  type: Notification['type'],
+  title: string,
+  message: string,
+  source: string,
+): Promise<Notification> {
+  const notif: Notification = {
+    id: randomUUID(),
+    type,
+    title,
+    message,
+    source,
+    timestamp: new Date().toISOString(),
+    read: false,
+    emailSent: false,
+  };
+
+  // Save to file
+  const notifs = loadNotifications();
+  notifs.push(notif);
+  saveNotifications(notifs);
+
+  // Send email to subscribed users
+  if (type === 'error' || type === 'warning') {
+    const users = loadUsers().filter(u => u.notifyOnError);
+    if (users.length > 0) {
+      try {
+        await smtpTransport.sendMail({
+          from: '"Eventify Monitor" <noreply@bshtech.net>',
+          to: users.map(u => u.email).join(', '),
+          subject: `[${type.toUpperCase()}] ${title}`,
+          html: `
+            <div style="font-family: sans-serif; max-width: 600px; margin: 0 auto;">
+              <div style="background: ${type === 'error' ? '#dc2626' : '#f59e0b'}; color: white; padding: 16px 24px; border-radius: 8px 8px 0 0;">
+                <h2 style="margin: 0; font-size: 18px;">${type === 'error' ? 'Error Alert' : 'Warning'}: ${title}</h2>
+              </div>
+              <div style="background: #f9fafb; padding: 24px; border: 1px solid #e5e7eb; border-top: none; border-radius: 0 0 8px 8px;">
+                <p style="margin: 0 0 12px; color: #374151;">${message}</p>
+                <p style="margin: 0 0 8px; color: #6b7280; font-size: 13px;"><strong>Source:</strong> ${source}</p>
+                <p style="margin: 0; color: #6b7280; font-size: 13px;"><strong>Time:</strong> ${new Date().toLocaleString()}</p>
+                <hr style="border: none; border-top: 1px solid #e5e7eb; margin: 16px 0;">
+                <p style="margin: 0; color: #9ca3af; font-size: 12px;">
+                  <a href="https://status.eventifyplus.com" style="color: #2563eb;">View Dashboard</a> | Eventify Server Monitor
+                </p>
+              </div>
+            </div>
+          `,
+        });
+        notif.emailSent = true;
+        // Update the saved notification
+        const updated = loadNotifications();
+        const idx = updated.findIndex(n => n.id === notif.id);
+        if (idx >= 0) {
+          updated[idx].emailSent = true;
+          saveNotifications(updated);
+        }
+        console.log(`[Notifications] Email sent to ${users.length} users for: ${title}`);
+      } catch (err) {
+        console.error(`[Notifications] Failed to send email:`, err);
+      }
+    }
+  }
+
+  return notif;
+}