docs(briefings): add diagram responsibilities to Qatux and project docs

- CLAUDE.md: add docs/diagrams/ to project structure, add diagram
  file conventions for D-record changes
- qatux.md: add priority 5 for diagram creation/updates
- workshop-start SKILL.md: add diagram step in wrap-up sequence

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -20,6 +20,7 @@ docs/
   briefings/          # Per-agent context briefings (maintained by Qatux)
   architecture/       # Technical architecture documents
   design/             # Game design documents
+  diagrams/           # d2 source + PNG renders (architecture, data-flow, entity, state, ui)
   sprints/            # Sprint briefings per team (server.md, client.md, copy.md, joint.md, etc.)
   workshops/          # Workshop briefs and outputs (per-workshop subdirectories)
 db/
@@ -144,6 +145,7 @@ Key rules:
 ### File conventions
 - Decisions: domain files in `decisions/` (see `decisions/README.md` for index)
 - Decision IDs: `D-NNN` (confirmed), `Q-NNN` (open questions), `R-NNN` (rejected)
+- Diagrams: `.d2` source + `.png` renders in `docs/diagrams/{category}/`. Create or update diagrams via `/d2-diagram` when D-records are added or modified.
 - Discussion rounds: numbered sequentially, archived to `docs/discussions/` when complete
 - Briefings: one per agent, updated after decision-producing rounds
 - Tickets: managed via `db/connectors/ticket` CLI or `/ticket` skill