chore(users): remove coordinator leftovers, tidy for userservice

- delete api/requests.http and ARCHITECTURE.md (coordinator content)
- rewrite README.md and .env.example for the userservice
- drop dead RunPeriodic (reaper machinery userservice has no use for)
- fix .gitignore/.dockerignore/.golangci.yml module + artifact names
- degeneralize stale copied comments that said "coordinator"

users/.gitignore

@@ -1,4 +1,4 @@
-/coordinator
+/userservice
 /bin/
 .env
 *.out