Implemented role-based UI handling

[Kaylahray]

Implement role-based UI and owner-only campaign actions

Changes Made

1. Created useRole Custom Hook

• Added src/hooks/useRole.js that returns { isAdmin, isUser } based on current user's role
• Provides reusable role checking across the application

2. Role-Based Navigation

• Updated Navbar to hide "Create Campaign" button for admin users
• Added "Admin Panel" link visible only to admin users
• Applied to both desktop and mobile navigation menus

3. Campaign Owner Actions

• Implemented Edit and Delete buttons in CampaignDetails page
• Buttons only visible to campaign owners (ownership check)
• Added confirmation dialog for delete action
• Styled with proper UI/UX considerations

4. Admin Route Protection

• Created AdminRoute component to protect admin-only routes
• Non-admin users are redirected to /dashboard
• Applied to /admin route in AppRouter

Acceptance Criteria Met

✅ Admin-only UI is hidden from regular users
✅ Owner-only actions are hidden from non-owners
✅ Clean separation of role-based vs ownership-based permissions

Closes #50