feat: add duplicate family detection

[bntvllnt]

Summary

• add deterministic duplicate function family detection with strict, mild, and weak modes
• expose duplicates CLI and find_duplicates MCP operation through the shared registry
• add CH-P1-04 chained CLI/MCP coverage, fixture clone families, docs, roadmap sync, and real-repo verifier coverage

Validation

• pnpm lint
• pnpm typecheck
• pnpm build
• pnpm test (456/456)
• pnpm verify:cli-real (pass=59 fail=0)
• git diff --check
• code-review artifact: /tmp/code-review-duplication-families.json (CLEAN, 89/89 hunks, 7/7 rules)