feat: backend API endpoints — admin market ops, users, bets, and market filters

[augustinemartins]

Closes #1077
Closes #1078
Closes #1089
Closes #1090

Summary

This PR implements 4 backend API endpoint groups for the BOXMEOUT prediction market:

1. Admin Market Resolution Endpoints

POST /api/admin/markets/:marketId/resolve, /cancel, /dispute-resolve

• All routes gated by requireAdmin middleware (x-admin-api-key header)
• Body validation for outcome/source/overrideOutcome fields
• Every action writes an AdminLog entry for audit trail
• Service layer handles Prisma updates atomically

2. User Profile Endpoints

GET /api/users/:address, PUT /api/users/:address

• GET returns profile data aggregated from bet history
• PUT requires Stellar wallet-signature verification via requireWalletAuth middleware
• Wallet auth uses x-wallet-signature and x-wallet-message headers with 5-min timestamp replay protection

3. Bets by Wallet Address

GET /api/bets/:address

• Returns all bets placed by a wallet address across markets
• Indexed on bettor for efficient queries
• Supports optional ?marketId filter

4. Market Bets with Outcome Filter

GET /api/markets/:id/bets

• Returns all bets for a market with optional ?outcome=yes|no filter
• Yes maps to FighterA, No maps to FighterB

Files Changed

File	Description
backend/src/api/middleware/auth.ts	Added requireWalletAuth middleware
backend/src/api/routes/market.routes.ts	Added 3 admin :marketId routes
backend/src/api/routes/user.routes.ts	New: GET/PUT /users/:address
backend/src/api/controllers/market.controller.ts	Added admin handlers + getMarketBetsHandler
backend/src/api/controllers/bet.controller.ts	Implemented getBetsByAddressHandler
backend/src/api/controllers/user.controller.ts	New: getUserHandler, updateUserHandler
backend/src/services/market.service.ts	Added resolveMarket, cancelMarket, resolveMarketDispute
backend/src/services/bet.service.ts	Implemented getBetsByAddress, getBetsByMarket
backend/src/services/user.service.ts	New: getUserByAddress, updateUser

Commits

1. aacf0dd feat: implement admin market service functions with audit logging
2. b34716e feat: wire admin market resolution endpoints with input validation
3. 3c557ff feat: implement bets-by-address and market-bets endpoints
4. 92cf285 feat: add user profile endpoints with wallet-signature authentication