fix: suppress notification sounds and zap animations for historical events

[barrydeen]

Summary

• Add notifInitialized flag to NotificationRepository that gates sound and zap animation emissions
• Reset flag to false at the start of subscribeDmsAndNotifications() and set true after EOSE arrives
• Prevents flood of notification sounds and stuck zap animations on cold start and force reconnect (30s+ background)

Test plan

• Force-close app with pending notifications, reopen — zero sounds on startup
• Wait for feed to load, receive a live reaction/zap — sound plays and animation shows
• Background app 30+ seconds, reopen — zero sounds during reload, live events trigger normally
• Switch accounts — flag resets cleanly via clear()