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>

docs/agents/domain.md

@@ -28,6 +28,14 @@ When your output names a domain concept (in an issue title, a refactor proposal,
 
 If the concept you need isn't in the glossary yet, that's a signal — either you're inventing language the project doesn't use (reconsider) or there's a real gap (note it for `/domain-modeling`).
 
+## New or conflicting terms
+
+When you meet a term that isn't in `CONTEXT.md`:
+
+- **A synonym of an existing term** (e.g. "proxy" for *gateway*): use the canonical term. There's nothing to edit or ask.
+- **A genuinely new concept:** add it to `CONTEXT.md` in the same change, as the term, a one- or two-sentence definition and an _Avoid_ list, with no values or config. Name the new term in your final message so the user can veto it.
+- **A conflict with an existing definition** (the code or the user uses a term differently than `CONTEXT.md` defines it): stop and ask the user. Redefining a term is their decision.
+
 ## Flag ADR conflicts
 
 If your output contradicts an existing ADR, surface it explicitly rather than silently overriding: