Add integration test for /api/markets

[Stranger-11]

Overview

This PR adds comprehensive integration tests for the /api/markets endpoints using supertest and Testcontainers-backed PostgreSQL, providing end-to-end coverage across all public market routes.

Related Issue

Closes #483

Changes

Integration test expansion

• [MODIFY] tests/integration/markets.test.ts expanded from 4 tests to 22 tests covering all public /api/markets endpoints
• Added requestContextStorage middleware and errorHandler middleware for realistic error envelope responses
• Added MarketSeed interface and enhanced seedMarkets helper supporting featured, featuredAt, and createdAt fields

Test Coverage

Group	Tests	What it covers
listing	3	Basic listing, archived exclusion, limit param
empty state	1	No markets returns empty data and null nextCursor
pagination	3	Multi-page cursor pagination, single-page, garbage cursor restart
single market by ID	2	Detail lookup by ID, 404 for non-existent ID
featured markets	3	featuredAt DESC ordering, exclusion of non-featured/archived, empty state
upcoming markets	3	resolutionTime ASC ordering, active exclusion, empty state
search markets	4	Full-text match, non-matching query, missing q param, empty q param
input validation	5	limit bounds (0, >100, non-numeric), default page size, correlationId, error details

Verification

TypeScript compilation passes. Linter has no errors in changed file. Integration tests require Docker (npm run test:integration). All tests follow established patterns from existing integration tests and use the same Testcontainers PostgreSQL setup.

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[greatest0fallt1me]

Green ✅ merging. Thanks for the contribution!