docs: add comprehensive README with Mermaid diagrams

chore: exclude runtime data files from repo

feat: add marketplace.json for local plugin installation

fix: restructure manifest — minimal plugin.json + separate hooks/hooks.json

feat: add 4 skills — /bootstrap, /audit-rules, /reflect, /health-check with templates

feat: add Tier 2 hooks + 3 reusable subagent definitions

feat: add 6 core hook scripts — session scan, compaction reinject, cognitive loop, session-end reflect, correction detect, post-commit nudge

feat: bootstrap plugin scaffold with manifest and data store