Add integration/unit test coverage for transaction history, search, holders, and sell payout

[CeceOs92]

Summary

Adds test coverage (and, where the feature didn't exist yet, the minimal implementation to support it) across four areas of the public API and pricing logic:

• Transaction history ordering — real-DB integration test seeding wallet activity out of chronological order and asserting the /wallets/:address/activity endpoint always returns entries newest-first, with sort order preserved across paginated pages.
• Creator search — real-DB integration test seeding overlapping display names (Alice/Alicia/Bob/Bobby) and asserting /creators?search= returns only correct partial, case-insensitive matches.
• Key holder sort order — /creators/:id/holders was missing key_count, share_percent, rank, and a deterministic tie-break. Added these (additive, non-breaking) plus a secondary ownerAddress asc sort, and a real-DB integration test verifying descending key-count order, alphabetical tie-break, required response fields, and that share_percent sums to 100% across all holders.
• Sell payout calculation — added computeSellPayout, the sell-side counterpart to computeBuyCost, applying the bonding curve formula and deducting the protocol fee. Added unit tests for 5%/0%/100% fee rates, the last-key-sell case, and the non-negative payout guarantee.

Changes

• src/modules/creators/creator-holders.service.ts — add key_count, share_percent, rank fields; add ownerAddress tie-break to sort.
• src/modules/creators/creator-holders.integration.test.ts, creator-holders-held-since.integration.test.ts — update fixtures for new required HolderRecord fields.
• src/utils/pricing.utils.ts — add computeSellPayout.
• src/utils/pricing.utils.test.ts — unit tests for computeSellPayout.
• src/__tests__/integration/wallet-activity-order.integration.test.ts — new.
• src/__tests__/integration/creator-holders-key-count-sort.integration.test.ts — new.
• src/modules/creators/creator-list-search-partial-name.integration.test.ts — new.

Closes #683
Closes #685
Closes #692
Closes #694

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