test(holders): add integration test for empty key holders list endpoint

[abimbolaalabi]

Overview

This PR adds a database-backed integration test that verifies the GET /api/v1/creators/:id/holders endpoint returns a 200 status with an empty items array when a creator exists but has no key holders, rather than a 404 or error.

Related Issue

Closes #662

Changes

🧪 Integration Test

• [ADD] src/__tests__/integration/creator-holders-empty-list.test.ts — seeds a creator with no KeyOwnership records and asserts:
  • Response status 200
  • items is an empty array
  • meta.total is 0 and meta.hasMore is false
  • Response shape is consistent with a non-empty holders list response

Verification Results

The controller logic (src/modules/creators/creator-holders.controller.ts) already returns 200 with { items: [], meta: { total: 0, hasMore: false } } when no holders exist — this test simply adds coverage for that code path end-to-end through the database.

Acceptance Criteria	Status
Response status 200 for a creator with no holders	✅
items is an empty array	✅
has_more is false	✅
Response shape consistent with a non-empty holders list response	✅

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