[Split #88320] PR 4 - Extract unread marker hooks

[rlinoz]

Goal: Extract useUnreadMarker and useMarkAsRead from ReportActionsList.

Scope:

• Add src/hooks/useUnreadMarker.ts
• Add src/hooks/useMarkAsRead.ts
• Update ReportActionsList.tsx
• Touch shouldDisplayNewMarkerOnReportAction.ts if the signature changes
• Add hook unit tests

Risk: Medium. Marker behavior is visible to users.

Depends on: #89764

Parent issue: #88320
Source plan: #88320 (comment)

Issue Owner

Current Issue Owner: @DylanDylann