Add ItemAcquireHistoryController (POST /item_acquire_history/info) with its
three DTOs and two integration tests (ordering + empty-viewer). The endpoint
reads ViewerAcquireHistory rows written by InventoryTransaction.CommitAsync,
ordered newest-first, capped at 300. Tests access doc.RootElement.histories
directly (no envelope wrapper in the test path — middleware skips non-UnityPlayer UA).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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