Build Admin Dashboard Shell + Volunteer Application Review Page

[vivjd]

Goal:
Build base admin dashboard and connect volunteer-application review.

Tasks:

• Protected Admin layout with navigation
• Volunteer Applications page fetching from /api/volunteer-applications
• Approve/Reject buttons triggering API calls and updating UI
• Display success/error toasts

Acceptance Criteria:

• Admin can log in and review applications
• UI updates dynamically after each action
• Non-admins blocked from dashboard