FRE-4495: Set up notification infrastructure (email, push, SMS)

- Created shared-notifications package with multi-channel support
- Implemented EmailService with Resend integration
- Implemented PushService with FCM/APNs support
- Implemented SMSService with Twilio integration
- Added NotificationService to orchestrate all channels
- Created notification types, configuration, and routes
- Added rate limiting and delivery tracking support
- Configured notification preferences management

Files:
- packages/shared-notifications/src/{types,config,services}/*.ts
- packages/shared-notifications/package.json
- apps/api/src/routes/notifications.routes.ts
- apps/api/package.json (updated dependencies)

packages/shared-notifications/src/config/notification.config.ts

@@ -0,0 +1,92 @@
+import { RateLimitConfig, NotificationChannel } from '../types/notification.types';
+
+// Resend configuration
+export interface ResendConfig {
+  apiKey: string;
+  fromEmail: string;
+  fromName: string;
+}
+
+// Firebase Cloud Messaging configuration
+export interface FCMConfig {
+  projectId: string;
+  privateKey: string;
+  clientEmail: string;
+  keyPath?: string; // Path to service account key file
+}
+
+// APNs configuration
+export interface APNsConfig {
+  keyPath: string; // Path to .p8 key file
+  keyId: string;
+  teamId: string;
+  bundleId: string;
+}
+
+// Twilio configuration
+export interface TwilioConfig {
+  accountSid: string;
+  authToken: string;
+  fromNumber?: string; // Optional default sender number
+}
+
+// Combined notification config
+export interface NotificationConfig {
+  resend: ResendConfig;
+  fcm?: FCMConfig;
+  apns?: APNsConfig;
+  twilio?: TwilioConfig;
+  rateLimits: {
+    email: RateLimitConfig;
+    push: RateLimitConfig;
+    sms: RateLimitConfig;
+  };
+}
+
+// Default rate limits
+export const defaultRateLimits: Record<NotificationChannel, RateLimitConfig> = {
+  [NotificationChannel.EMAIL]: {
+    maxPerWindow: 100,
+    windowMs: 60 * 60 * 1000, // 1 hour
+    key: 'user',
+  },
+  [NotificationChannel.PUSH]: {
+    maxPerWindow: 50,
+    windowMs: 60 * 60 * 1000, // 1 hour
+    key: 'user',
+  },
+  [NotificationChannel.SMS]: {
+    maxPerWindow: 20,
+    windowMs: 60 * 60 * 1000, // 1 hour
+    key: 'user',
+  },
+};
+
+// Load config from environment variables
+export function loadNotificationConfig(): NotificationConfig {
+  return {
+    resend: {
+      apiKey: process.env.RESEND_API_KEY!,
+      fromEmail: process.env.RESEND_FROM_EMAIL || 'noreply@shieldsai.com',
+      fromName: process.env.RESEND_FROM_NAME || 'ShieldAI',
+    },
+    fcm: process.env.FCM_PROJECT_ID ? {
+      projectId: process.env.FCM_PROJECT_ID,
+      privateKey: process.env.FCM_PRIVATE_KEY!.replace(/\\n/g, '\n'),
+      clientEmail: process.env.FCM_CLIENT_EMAIL!,
+      keyPath: process.env.FCM_KEY_PATH,
+    } : undefined,
+    apns: process.env.APNS_KEY_PATH ? {
+      keyPath: process.env.APNS_KEY_PATH,
+      keyId: process.env.APNS_KEY_ID!,
+      teamId: process.env.APNS_TEAM_ID!,
+      bundleId: process.env.APNS_BUNDLE_ID!,
+    } : undefined,
+    twilio: process.env.TWILIO_ACCOUNT_SID ? {
+      accountSid: process.env.TWILIO_ACCOUNT_SID!,
+      authToken: process.env.TWILIO_AUTH_TOKEN!,
+      fromNumber: process.env.TWILIO_FROM_NUMBER,
+    } : undefined,
+    rateLimits: defaultRateLimits,
+  };
+}