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)

apps/api/package.json

@@ -13,6 +13,7 @@
     "@fastify/helmet": "^13.0.2",
     "@shieldsai/shared-auth": "*",
     "@shieldsai/shared-db": "*",
+    "@shieldsai/shared-notifications": "*",
     "@shieldsai/shared-utils": "*",
     "fastify": "^4.25.0",
     "fastify-plugin": "^4.5.0"