Fix/trade indexer and pagination helpers

[Mosas2000]

Summary

Testing

• pnpm lint
• pnpm build
• pnpm exec prisma generate when schema or generated types changed

Checklist

This PR resolves issues #619, #625, #630, and #631.

1. Closes Add integration test for trade indexer correctly persisting buy events from Soroban transaction stream #619: Trade Indexer Buy Event Persistence & Integration Test
   Added Trade Prisma model in prisma/schema/trade.prisma with a compound unique index on (ledger, txHash) to support idempotent event writes.
   Added processTradeEvent service in src/modules/indexer/trade-indexer.service.ts to validate required fields (buyer, creator_id, quantity, price, ledger, tx_hash, timestamp), persist valid events, skip duplicate events, and warn-log malformed inputs.
   Created integration test src/modules/indexer/trade-indexer.integration.test.ts to verify field accuracy, idempotency, malformed event skipping, and warn logging.
2. Closes Add helper for paginating database queries with a keyset cursor on the trade history table #625: Keyset Cursor Pagination Helper for Trade History
   Added queryTradesPage(creatorId: string, cursor: string | null, limit: number, db: any) helper in src/utils/trade-pagination.utils.ts.
   Encodes/decodes (ledger, tx_hash) using HMAC-signed base64url cursors for stable keyset pagination ordered by ledger desc, txHash desc.
   Added unit tests in src/utils/tests/trade-pagination.utils.test.ts asserting first page ordering, cursor page traversal, has_more correctness, and record uniqueness across pages.
3. Closes Add integration test for creator detail endpoint returning correct holder count after sequential buys and sells #630: Creator Detail Holder Count Integration Test
   Updated httpGetCreatorStats in src/modules/creators/creators.controllers.ts and mapPublicCreatorStats in src/modules/creators/creators.stats.ts to query active key holders (KeyOwnership records with balance > 0) and expose both holderCount and holder_count.
   Created integration test src/modules/creators/creator-detail-holder-count-sequential.integration.test.ts verifying holder count changes across sequential buys and sells across multiple wallets (0 → 1 → 2 → 2 → 1 → 0).
4. Closes Add helper for formatting structured log fields consistently across all server modules #631: Shared Log Fields Formatting Builder
   Added buildLogFields(base: LogFields): Record<string, unknown> in src/utils/log-fields.utils.ts to enforce snake_case keys, ISO 8601 timestamps, and truncation of string values exceeding 500 characters with a [TRUNCATED] suffix.
   Applied buildLogFields across server log call sites.
   Added unit tests in src/utils/tests/log-fields.utils.test.ts verifying key conversion, ISO timestamp formatting, and string truncation rules.

• Linked issue or backlog item
• No secrets or live credentials added
• Docs updated if setup or env changed
• Change is scoped to one problem

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