Frontend: Wallet profile modal on address click

Context

Replace participant address explorer links with wallet stats modal. Parent epic: #238 (closed).

Relevant files

• frontend/src/components/AddressInline.tsx
• frontend/src/components/MegaScannerAddressLink.tsx — explorer for contracts only
• New: WalletProfileModal.tsx, useWalletStats.ts
• frontend/src/lib/indexerApi.ts

Acceptance criteria

• Click participant address → modal with stats from GET /v1/arena/wallet/{address}/stats
• Sections: Overview, Podium wins, Spending, XP/Level, WarBow, Referrals, Fun facts
• Secondary link "View on explorer" inside modal
• Loading/error/offline states (#96 (closed))
• Mobile layout (#201 (closed))

Verification checklist

• Manual QA on live buy row + podium rankings
• Keyboard focus trap + WCAG (#97 (closed))