feat(api): implement GetEvent gRPC handler

[Depo-dev]

Summary

EventsServiceImpl::get_event currently returns Status::unimplemented. Needs a SELECT by UUID with proper not-found handling.

Acceptance Criteria

• Parse the UUID from GetEventRequest.id; return Status::invalid_argument if malformed
• SELECT * FROM soroban_events WHERE id = $1
• Return Status::not_found if no row matches
• Map row → proto Event message
• Integration test: fetch existing UUID returns correct event; fetch unknown UUID returns NOT_FOUND

Files

crates/api/src/services/events.rs