feat: add optional architecture visualizer

[ryan-zheng-teki]

Summary

• add an architecture_visualizer team member for explicitly requested human-facing Mermaid views
• keep visualization outside the primary workflow as a non-blocking side request
• produce one canonical architecture-diagrams.md derived from the current solution package
• prioritize subsystem ownership maps, business/data-flow sequences, and proportional boundary detail
• add concrete component, sequence, interface, and lifecycle examples
• preserve authoritative solution artifacts and normal architecture-review routing

Validation

• skill-creator quick validation passes
• JSON configuration and member/skill references validate
• git diff --check passes