test(#502): add integration test for activity feed cursor pagination

[Sam-Rytech]

Description

This PR resolves the missing integration test and cursor pagination functionality for the wallet activity feed.

Changes included:

• Updated WalletActivityQuerySchema to accept an optional cursor string.
• Modified fetchWalletActivity to decode the cursor, adjust the Prisma pagination parameters to use cursor with skip: 1 when provided, and encode a nextCursor for the last item.
• Updated httpGetWalletActivity to expose nextCursor in the response envelope's meta block.
• Added a full integration test (wallet-activity-cursor-pagination.integration.test.ts) that asserts:
  • First page returns a valid next cursor.
  • Second page fetches correctly using the cursor, with no duplicates or skipped events across the two pages.

Closes #502

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