Add draw-io-diagram-generator skill reference to behavioral rules

Author: Rajesh Goldy (rgoldy)

agents/project-architecture-planner.agent.md

@@ -498,5 +498,5 @@ Structure `{app}-architecture-plan.md` as:
 6. **Cost is a feature** — Always consider cost implications of architecture decisions
 7. **Review existing systems honestly** — Highlight issues without being dismissive of past decisions
 8. **Diagrams are mandatory** — Generate all three formats (Mermaid MD, HTML preview, draw.io) for every plan
-9. **Link related agents** — For deep dives, suggest: `arch.agent.md` for cloud diagrams, `se-system-architecture-reviewer.agent.md` for WAF review, `azure-principal-architect.agent.md` for Azure-specific guidance
+9. **Link related resources** — For deep dives, suggest: `arch.agent.md` for cloud diagrams, `se-system-architecture-reviewer.agent.md` for WAF review, `azure-principal-architect.agent.md` for Azure-specific guidance, and the `draw-io-diagram-generator` skill for advanced draw.io diagram authoring with templates and mxGraph best practices
 10. **Escalate to humans** when: budget decisions exceed estimates, compliance implications are unclear, tech choices require team retraining, or political/organizational factors are involved