feat: R5 improvements — collaborative editing, multi-tenant, expanded ops troubleshooting

docs: fix plugin install commands to use marketplace flow

fix: correct plugin.json skills format and add marketplace.json

docs: add Claude Code plugin install method as recommended option

docs: add detailed test methodology, sample results, and workflow scores

feat: add TS examples, operational troubleshooting, and context-aware workflows

feat: improve reference coverage, add code examples, workflow guides, and cross-skill bridges

feat: add design pattern skills, Mermaid diagrams, R3 quality improvements, and install scripts

docs: document interactive clarifying questions feature in README

feat: add interactive clarifying questions to all 3 skills

docs: add batch 5 expert test results to quality validation

feat: add 4 reference files and expand coverage for 100-problem test suite

fix: reference paths and test feedback improvements

feat: system design advisor skills for Claude Code and Cursor