`provision_merchant` swallows the underlying error (no logging)

[Darkdruce]

Summary

On DB failure the handler maps the error to a generic 500 via map_err(|_| ...), discarding the cause, unlike the AppError path which logs.

Location

• src/api/mod.rs:145-152 vs src/api/payments.rs:45-54 (From<anyhow::Error> logs)

Details & impact

Provisioning failures are undiagnosable from logs.

Suggested fix

Log the error (reuse AppError) before returning 500.

Acceptance criteria

• Provisioning failures are logged with context.