[FE-37] Build Member Tier Badge component for Bronze/Silver/Gold/Platinum tiers

[devwums]

Problem

There is no visual representation of a member's tier (Bronze/Silver/Gold/Platinum) anywhere in the UI. The tier concept exists on the backend but is invisible to members.

Proposed Solution

Create frontend/cntr/MemberTierBadge/MemberTierBadge.tsx. Props: tier: 'BRONZE' | 'SILVER' | 'GOLD' | 'PLATINUM'. Renders a badge with a tier-specific colour (Bronze: #CD7F32, Silver: #C0C0C0, Gold: #FFD700, Platinum: #E5E4E2) and a Medal or Award icon from lucide-react. All implementation must live inside frontend/cntr/.

Acceptance Criteria

• File at frontend/cntr/MemberTierBadge/MemberTierBadge.tsx
• All 4 tier colours applied (use Tailwind arbitrary values or inline style)
• tier prop is a TypeScript union type — no raw strings accepted
• Icon from lucide-react displayed alongside the tier label
• Test in frontend/cntr/MemberTierBadge/MemberTierBadge.test.tsx rendering all 4 tiers