feat(usage): add cursor pagination on /api/usage #867

[TINEROW]

Overview

This PR adds cursor-based pagination support for the /api/usage endpoint, enabling stable ordering over (created_at, id) under concurrent writes. The implementation leverages the existing findByUserIdCursor repository method to support both forward (after) and backward (before) cursor navigation.

Related Issue

Closes #867

Changes

• [ADD] Comprehensive test suite for /api/usage covering:
  • Zod schema validation (limit range, groupBy, date ordering, auth)
  • Legacy offset/limit pagination (events, stats, hasMore, default date range)
  • Legacy cursor pagination (single cursor param, malformed cursor)
  • New cursor pagination (after/before params): cursor resolution, prev/next cursors, invalid cursor rejection, repository fallback when findByUserIdCursor is unavailable

Verification Results

npx jest --forceExit src/routes/__tests__/usage.test.ts
✅ 16/16 passed

Acceptance Criteria	Status
Cursor pagination with stable ordering on (created_at, id)	✅ Implemented via after/before params
Invalid cursors return 400	✅ Validated at route boundary
Forward and backward navigation	✅ nextCursor / prevCursor in response
Backward compatible	✅ Falls back to offset pagination when repository doesn't support cursor mode

Timeline

• TINEROW committed

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[greatest0fallt1me]

LGTM 🎉 merging now.