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/package.json

@@ -0,0 +1,28 @@
+{
+  "name": "@shieldsai/shared-notifications",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "main": "./src/index.ts",
+  "types": "./src/index.ts",
+  "exports": {
+    ".": {
+      "import": "./src/index.ts",
+      "types": "./src/index.ts"
+    }
+  },
+  "scripts": {
+    "build": "tsc",
+    "lint": "eslint src/"
+  },
+  "dependencies": {
+    "resend": "^6.12.2",
+    "firebase-admin": "^13.2.0",
+    "twilio": "^5.4.0",
+    "zod": "^4.3.6"
+  },
+  "devDependencies": {
+    "@types/node": "^25.6.0",
+    "typescript": "^5.3.3"
+  }
+}