docs(agents): add writing-docs guide and new-term procedure

docs/agents/writing-docs.md holds the doc/comment rules and done-check,
reached via a pointer in CLAUDE.md (AGENTS.md and QWEN.md import it).
docs/agents/domain.md gains the procedure for new or conflicting terms.

Refs #55 (agent guide #62)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -8,6 +8,10 @@ Issues live as Gitea issues on `git.arthurerlich.de` (repo `haylan/LLM-Server`);
 
 Single-context: `CONTEXT.md` + `docs/adr/` at the repo root. See `docs/agents/domain.md`.
 
+### Writing docs
+
+Before editing `README.md`, `docs/`, or a comment in `docker-compose.yml` / `.env.example` / `scripts/`, read `docs/agents/writing-docs.md`.
+
 ### Deploying changes
 
 The running stack lives on a separate box (the R9700 server), not wherever this repo is being edited. After **any** change to `docker-compose.yml`, `.env.example`, or a script under `scripts/`, commit/push it, then run `./scripts/update.sh` on the server to apply it — don't just describe the change as done. If this session doesn't have shell access to the server, say so explicitly and tell the user to run it themselves rather than leaving it unsaid.