feat: add wallet activity feed endpoint (#424)

[Nanle-code]

Closes #424

Acceptance Criteria ✅ All Met

1. Returns all buy and sell events for the wallet in reverse chronological order

   • ✅ Service filters for KEY_BOUGHT and KEY_SOLD activity types
   • ✅ Ordered by createdAt: 'desc' (most recent first)

2. Each event includes the price and fee at the time of the trade

   • ✅ Response includes price_at_trade, fee_paid, and ledger_sequence from stored payload
   • ✅ Not current price - historical data from indexed events

3. type=buy or type=sell filter returns only matching events

   • ✅ Query param type mapped to internal ActivityType enum
   • ✅ Service filters accordingly when provided

4. creator_id filter returns only trades for that creator

   • ✅ Query param creator_id added to where clause
   • ✅ Filters by creatorId when provided

5. Returns empty array (not 404) for a valid wallet with no activity

   • ✅ Service returns [[], 0] when no rows found
   • ✅ Controller returns 200 with empty items array
   • ✅ Test verifies this behavior

6. Returns 400 for a malformed Stellar address

   • ✅ Uses StellarAddressSchema for validation
   • ✅ Returns 400 with validation error on invalid format
   • ✅ Test covers malformed address case

7. Pagination works correctly across large trade histories

   • ✅ Uses offset/limit pagination with Prisma
   • ✅ Returns proper metadata (limit, offset, total, hasMore)
   • ✅ Tests verify pagination behavior

8. Integration test covers: mixed history, type filter, creator filter, empty wallet

   • ✅ All 13 integration tests passing
   • ✅ Covers mixed history, type filters, creator filter, empty wallet, malformed address, pagination, and error handling