Add wallet activity feed endpoint for full trade history across all creators

[Chucks1093]

Summary

A fan who has been active on the platform — buying and selling keys across multiple creators — has no way to review their own history. They need a single endpoint that shows every trade their wallet has made in chronological order, across all creators, so they can track their activity, calculate their own returns, and understand their trading patterns.

Scope

• Add GET /wallets/:address/activity endpoint
• Returns paginated list of trade events: { type (buy|sell), creator_id, creator_handle, amount, price_at_trade, fee_paid, ledger_sequence, timestamp }
• Default sort is most recent first
• Support type filter param to show only buys or only sells
• Support creator_id filter param to see activity for a specific creator only
• Data is sourced from the indexed trade event history

Acceptance Criteria

• Returns all buy and sell events for the wallet in reverse chronological order
• Each event includes the price and fee at the time of the trade (not current price)
• type=buy or type=sell filter returns only matching events
• creator_id filter returns only trades for that creator
• Returns empty array (not 404) for a valid wallet with no activity
• Returns 400 for a malformed Stellar address
• Pagination works correctly across large trade histories
• Integration test covers: mixed history, type filter, creator filter, empty wallet

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Coordinate on Telegram

[KingDavid9999]

Hey, I'd like to claim this issue!
I've reviewed the scope and acceptance criteria.
My plan:

Address validation: Check for an existing Stellar address validation util in the codebase; if none exists, add a shared middleware that returns 400 on malformed input, reusable across wallet endpoints.

Query layer: Build a cross-creator trade event query filtered by wallet address, with optional type and creator_id WHERE conditions. I'll use ledger_sequence as the pagination cursor for stable reverse-chronological ordering.

Historical price/fee: Confirm that price_at_trade and fee_paid are stored on the indexed trade event records at write time (not derived from current state). If there's a gap, I'll flag it before proceeding.

Endpoint: Wire up GET /wallets/:address/activity with the query, filter params, and paginated response shape matching the spec.

Integration tests: Cover all four specified scenarios: mixed history, type filter, creator_id filter, and empty wallet returning [].
I've contributed to this codebase before and have prior experience building paginated activity feed endpoints on Stellar-based platforms.