feat: paginated active markets + three indexer event handlers

[proverbs31ziggo-a11y]

Closes #1069
Closes #1070
Closes #1071
Closes #1072

Summary

This PR implements four backend features for the BOXMEOUT platform:

1. Paginated Active Markets (d04af0b)

Returns active markets from DB, paginated, most-recent-first.

• Enforces a max pageSize of 100 via MAX_PAGE_SIZE constant
• Returns total count alongside data for frontend pagination UI (PaginatedResult<T>)
• Sorts by createdAt descending (most-recent-first)
• Cleans up duplicate imports, consolidates on db client
• Updates controller to use pageSize param and return PaginatedResult directly

2. Decode market_cancelled Events (c810b41)

Decodes market_cancelled events and sets market status to cancelled.

• Registers MarketCancelled case in processLedger event routing
• Implements handleMarketCancelledEvent to call updateMarketStatus(id, "Cancelled")
• Covered by unit test with mock event payload

3. Decode winnings_claimed Events (b6b14f0)

Decodes winnings_claimed and refund_claimed events, marking BetModel.claimed = true.

• Adds markBetClaimedByMarketAndBettor in bet.service.ts using atomic updateMany
• Splits old handleWinnersClaimedEvent into separate handleWinningsClaimedEvent and handleRefundClaimedEvent
• Matches the correct bet row via (marketId, bettor) from the event body
• Includes comprehensive unit tests (50 tests pass across 2 test suites)

4. Decode resolution_disputed Events (4077ba8)

Decodes resolution_disputed events, sets market status to disputed.

• Adds updateMarketStatus(id, "Disputed") call in handleDisputeEvent for DisputeRaised
• Stores dispute reason in the Dispute table for admin review UI
• Covered by unit tests verifying both dispute creation and status update

Files Changed

File	Changes
backend/src/services/market.service.ts	Paginated result, max pageSize, cleanup
backend/src/api/controllers/market.controller.ts	Use pageSize + PaginatedResult
backend/src/services/bet.service.ts	markBetClaimedByMarketAndBettor (atomic)
backend/src/services/indexer.service.ts	MarketCancelled, WinningsClaimed, RefundClaimed, DisputeRaised handlers
backend/src/services/__tests__/indexer.service.test.ts	Tests for all 4 event handlers
backend/src/services/indexer.service.test.ts	Updated claim handler tests

Testing

All 50 tests pass across both test suites.

npx jest --runInBand --testPathPattern="indexer.service"
# Test Suites: 2 passed, 2 total
# Tests:       50 passed, 50 total