Get current user

Reads `users` on every call so that an email change is reflected without forcing a session refresh. The handler is intentionally tenant-agnostic — `users` is global per ADR 0008.

curl -X GET "https://api.monitoring.crahe-arthur.com/api/v1/auth/me"

{
  "id": "018f7b9a-57dd-4748-9e13-6e3e3e5b9eaf",
  "email": "admin@acme.example",
  "fullName": "Arthur Crahé"
}