AI roadmap (fase 0): CLAUDE.md + skills propias del proyecto (#381)

[ngarbezza]

Summary

• Add ## Project DNA section to CLAUDE.md with the three core values of the project: zero-dependency (scoped to lib/ and bin/), no dark magic, and OOP in the Smalltalk spirit. Acts as a filter for AI assistants and contributors.
• Add ## Contributing conventions section to CLAUDE.md with: mandatory self-testing, one PR one concept, and the gate to run npm test + npm run lint before opening a PR.
• Add npm run test:coverage and npm run test:mutation to the ## Commands section.
• Create .claude/skills/add-assertion/SKILL.md: a conversational 5-step skill (/add-assertion) that guides contributors through adding a new assertion — from understanding the need to self-testing — while enforcing the project's DNA at every step.

Closes #381.

Test plan

• Verify CLAUDE.md renders correctly on GitHub
• Verify .claude/skills/add-assertion/SKILL.md is invocable as /add-assertion in a Claude Code session on this repo
• Run npm test to confirm no regressions
• Run npm run lint to confirm no linting issues

🤖 Generated with Claude Code