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/.golangci.yml

@@ -51,4 +51,4 @@ formatters:
   settings:
     goimports:
       local-prefixes:
-        - github.com/emil28092005/SciMesh/coordinator
+        - github.com/emil28092005/SciMesh/users