FRE-4521 Implement Redis integration for rate limiting and deduplication

- Add ioredis dependency for Redis connection pooling
- Create RedisService singleton with connection management
- Add Redis config (url, dedupWindowSeconds) to notification.config.ts
- Implement NotificationService.checkRateLimit using Redis INCR+EXPIRE
- Implement NotificationService.deduplicateNotification using Redis SET/NX
- Add configurable rate limit windows and thresholds via env vars
- Add 29 unit tests covering Redis operations, rate limiting, and dedup
- All tests pass, TypeScript compiles cleanly for new files

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

@@ -25,6 +25,11 @@ export const NotificationConfigSchema = z.object({
     emailPerMinute: z.number().default(60),
     smsPerMinute: z.number().default(30),
     pushPerMinute: z.number().default(100),
+    windowSeconds: z.number().default(60),
+  }),
+  redis: z.object({
+    url: z.string().default('redis://localhost:6379'),
+    dedupWindowSeconds: z.number().default(300),
   }),
 });
 
@@ -55,5 +60,10 @@ export const loadNotificationConfig = (): NotificationConfig => ({
     emailPerMinute: parseInt(process.env.EMAIL_RATE_LIMIT || '60', 10),
     smsPerMinute: parseInt(process.env.SMS_RATE_LIMIT || '30', 10),
     pushPerMinute: parseInt(process.env.PUSH_RATE_LIMIT || '100', 10),
+    windowSeconds: parseInt(process.env.RATE_LIMIT_WINDOW_SECONDS || '60', 10),
+  },
+  redis: {
+    url: process.env.REDIS_URL || 'redis://localhost:6379',
+    dedupWindowSeconds: parseInt(process.env.DEDUP_WINDOW_SECONDS || '300', 10),
   },
 });