Fix #72: add user info to auth log events

[mishankov]

Closes #72

Summary

• enrich authenticated request-wide log events in the auth middleware
• add user.id and user.username attributes when a wide event is present
• keep the existing userId context enrichment for regular context-aware logs
• add a focused auth middleware test covering the new wide-event behavior

Testing

• go test ./auth
• task test

Code Review

• Reviewed the branch diff against origin/main
• No material blocker findings were identified

Notes

• task lint currently fails due to pre-existing noctx findings in auth/handler_delete_test.go, outside this change set