- Add endpoint to search users by email (case-insensitive)
- Limit results to 10 for autocomplete purposes
- Require VIEW_ALL_EXCHANGES permission (admin only)
- Add tests for search functionality and access control
The agreed_price depends on trade direction (buy/sell) and must be
calculated on the frontend. Returning a buy-side-only agreed_price
from the API was misleading and unused.
Frontend already calculates the direction-aware price correctly.