Sprint 66: In-App Notification Logic Verification & FEEDBACK_RESOLVED Propagation Fix

Decisions

Context: In Sprint 64, FEEDBACK_RESOLVED was added to the Identity entity but was not propagated to Gateway enum and Frontend type/icon, causing feedback resolution notifications to appear with type mismatch and only the default Bell icon.
Choice: Apply updates across Gateway enum, Frontend Notification type union, NotificationBell TYPE_ICON/TYPE_ROUTE, and NotificationToast TYPE_ICON
Alternatives: None
Code Paths: services/gateway/src/common/types/identity.types.ts, frontend/src/lib/api.ts, frontend/src/components/layout/NotificationBell.tsx, frontend/src/components/ui/NotificationToast.tsx

Where: Identity entity → Gateway types → Frontend api.ts → NotificationBell (TYPE_ICON, TYPE_ROUTE) → NotificationToast (TYPE_ICON)
When to Reuse: All 5 files must be updated whenever a new notification type is added

Symptom: Feedback resolution notification shows default Bell icon on frontend, FEEDBACK_RESOLVED route not specified
Root Cause: Enum was only added to Identity entity, missed Gateway/Frontend synchronization
Fix: Update all 5 files following P1 checklist. Must apply the same pattern for future new type additions.

Symptom: DEADLINE_REMINDER, MEMBER_JOINED, MEMBER_LEFT, STUDY_CLOSED (4 types) showing Bell fallback icon in NotificationToast
Root Cause: 9 icon types registered in NotificationBell but only 5 registered in NotificationToast (missed in initial implementation)
Fix: Add 5 missing types + FEEDBACK_RESOLVED to NotificationToast TYPE_ICON (total 10 types fully covered)