feat: game lobby service

CLAUDE.md

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+# Galaxy Game — Project Conventions
+
+This repository hosts the Galaxy Game project.
+
+## Sources of truth
+
+- `ARCHITECTURE.md` — global architecture, project-wide rules
+  and links to the implemented services.
+- `galaxy/<service>/README.md` - service conventions and agreements
+  for the implemented or planned to be implemented service.
+
+## Planning of service implementation and Implementing Plan
+
+- `galaxy/<service>/PLAN.md` — staged implementation plan for the service.
+  May be already complete and resides for historical reasons.
+- `galaxy/<service>/docs/` — per-stage decision records
+  (one file per decision, re-organized after full implementation
+  of `PLAN.md`).
+
+## Decision records when implementing stages from PLAN.md
+
+- Stage-related discussion and decisions do NOT live in `README.md` or
+  `ARCHITECTURE.md`. Those files describe the current state, not the history.
+- Each non-trivial decision gets its own `.md` under the module's `docs/`,
+  referenced from the relevant `README.md`.
+- Any agreement reached during interactive planning that is not obvious from
+  the code must be captured — either as a decision record or as an entry in
+  the module's README.
+
+## Scope of PLAN.md changes
+
+The existing codebase of `galaxy/<service>` may be modified or extended when a
+plan stage requires it. All such changes must be covered by new or updated tests
+and reflected in documentation when they affect documented behavior.
+
+## Documentation discipline
+
+- Code and docs are kept in sync. If an implementation changes behavior
+  described in a `.md` or `.yaml` file, update that file in the same patch.
+- If existing docs are incomplete or wrong for behavior you are already
+  touching, fix them in the same patch.
+- Do not silently remove commitments from `galaxy/<service>/README.md`
+  or `galaxy/<service>/docs/*.md`. When a rule changes, either update it
+  in place with the new agreement, or move the section to a more appropriate
+  doc with a reference kept.
+- Cross-module impact: if a new agreement requires changes in
+  already-implemented modules, make those changes — code, tests, docs — in
+  the same patch, and record the new rule in `ARCHITECTURE.md`.
+
+## Dependencies
+
+- Before adding a new module, check its upstream repository for the latest
+  stable version and use that.
+- When a well-maintained library clearly outperforms stdlib for a concrete
+  need, do not adopt it silently — propose a short list of 1+ candidates for
+  the user to pick. Default remains stdlib.
+
+## Language
+
+- All code, comments, identifiers, commit messages, docs, and filenames are
+  written in English.
+- User-facing chat responses follow the Russian-translation rule from the
+  user-level `CLAUDE.md`.